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Brasilicardin A (1) consists of an unusual anti/syn/anti‐perhydrophenanthrene skeleton with a carbohydrate side chain and an amino acid moiety. It exhibits potent immunosuppressive activity, yet its mode of action differs from standard drugs that are currently in use. Further pre‐clinical evaluation of this promising, biologically active natural product is hampered by restricted access to the ready material, as its synthesis requires both a low‐yielding fermentation process using a pathogenic organism and an elaborate, multi‐step total synthesis. Our semi‐synthetic approach included a) the heterologous expression of the brasilicardin A gene cluster in different non‐pathogenic bacterial strains producing brasilicardin A aglycone (5) in excellent yield and b) the chemical transformation of the aglycone 5 into the trifluoroacetic acid salt of brasilicardin A (1 a) via a short and straightforward five‐steps synthetic route. Additionally, we report the first preclinical data for brasilicardin A., The development of a heterologous producer strain that enables the sustainable production of the stereochemically complex natural products brasilicardin C and E at excellent rates is presented. The semi‐synthetic approach allows an efficient gram‐scale conversion of brasilicardin E into the potent immunosuppressant brasilicardin A for which the first preclinical data are reported.

The bacteria of the genus Streptomyces are among the most important producers of biologically active secondary metabolites. Moreover, recent genomic sequence data have shown their enormous genetic potential for new natural products, although many new biosynthetic gene clusters (BGCs) are silent. Therefore, efficient and stable genome modification techniques are needed to activate their production or to manipulate their biosynthesis towards increased production or improved properties. We have recently developed an efficient markerless genome modification system for streptomycetes based on positive blue/white selection of double crossovers using the bpsA gene from indigoidine biosynthesis, which has been successfully applied for markerless deletions of genes and BGCs. In the present study, we optimized this system for markerless insertion of large BGCs. In a pilot test experiment, we successfully inserted a part of the landomycin BGC (lanFABCDL) under the control of the ermEp* promoter in place of the actinorhodin BGC (act) of Streptomyces lividans TK24 and RedStrep 1.3. The resulting strains correctly produced UWM6 and rabelomycin in twice the yield compared to S. lividans strains with the same construct inserted using the PhiBT1 phage-based integration vector system. Moreover, the system was more stable. Subsequently, using the same strategy, we effectively inserted the entire BGC for mithramycin (MTM) in place of the calcium-dependent antibiotic BGC (cda) of S. lividans RedStrep 1.3 without antibiotic-resistant markers. The resulting strain produced similar levels of MTM when compared to the previously described S. lividans RedStrep 1.3 strain with the VWB phage-based integration plasmid pMTMF. The system was also more stable. KEY POINTS: • Optimized genome editing system for markerless insertion of BGCs into Streptomyces genomes • Efficient heterologous production of MTM in the stable engineered S. lividans strain.

We previously developed an efficient deletion system for streptomycetes based on the positive selection of double-crossover events using bpsA, a gene for producing the blue pigment indigoidine. Using this system, we removed interfering secondary metabolite clusters from Streptomyces lividans TK24, resulting in RedStrep strains with dramatically increased heterologous production of mithramycin A (up to 3-g/l culture). This system, however, required a time-consuming step to remove the resistance marker genes. In order to simplify markerless deletions, we prepared a new system based on the plasmid pAMR18A. This plasmid contains a large polylinker with many unique restriction sites flanked by apramycin and kanamycin resistance genes and the bpsA gene for selecting a double-crossover event. The utility of this new markerless deletion system was demonstrated by its deletion of a 21-kb actinorhodin gene cluster from Streptomyces lividans TK24 with 30% efficiency. We used this system to efficiently remove the matA and matB genes in selected RedStrep strains, resulting in biotechnologically improved strains with a highly dispersed growth phenotype involving non-pelleting small and open mycelia. No further increase in mithramycin A production was observed in these new RedStrep strains, however. We also used this system for the markerless insertion of a heterologous mCherry gene, an improved variant of the monomeric red fluorescent protein, under the control of the strong secretory signal sequence of the subtilisin inhibitor protein, into the chromosome of S. lividans TK24. The resulting recombinant strains efficiently secreted mCherry into the growth medium in a yield of 30 mg/l.

Brasilicardin A (BraA) is a promising immunosuppressive compound produced naturally by the pathogenic bacterium Nocardia terpenica IFM 0406. Heterologous host expression of brasilicardin gene cluster showed to be efficient to bypass the safety issues, low production levels and lack of genetic tools related with the use of native producer. Further improvement of production yields requires better understanding of gene expression regulation within the BraA biosynthetic gene cluster (Bra‐BGC); however, the only so far known regulator of this gene cluster is Bra12. In this study, we discovered the protein LysRNt, a novel member of the LysR‐type transcriptional regulator family, as a regulator of the Bra‐BGC. Using in vitro approaches, we identified the gene promoters which are controlled by LysRNt within the Bra‐BGC. Corresponding genes encode enzymes involved in BraA biosynthesis as well as the key Bra‐BGC regulator Bra12. Importantly, we provide in vivo evidence that LysRNt negatively affects production of brasilicardin congeners in the heterologous host Amycolatopsis japonicum. Finally, we demonstrate that some of the pathway related metabolites, and their chemical analogs, can interact with LysRNt which in turn affects its DNA‐binding activity.

La presente investigación expone un conjunto de estándares compuestos de distintas dimensiones e indicadores de rendimiento para evaluar la competencia en la comunicación científica en profesores universitarios mexicanos. El estudio se integró por distintas fases complementarias y subsecuentes: (i) investigación documental sobre elementos normativos y teóricos que sustentan la identificación inicial de indicadores de rendimiento de evaluación comunicación científica; (ii) validación de información por 32 investigadores expertos en ciencias; (iii) validación de información por 62 expertos en alfabetización informacional (ALFIN); y (iv) derivación de un conjunto de estándares, mismos que fueron probados en 28 profesores universitarios del área de las ciencias químicas con potencialidad científica. Los resultados de la investigación definieron un conjunto de estándares integrados por ocho dimensiones y 34 indicadores de rendimiento, para posteriormente probar su funcionalidad diagnosticando niveles individuales y colectivos de competencia en comunicación científica, favoreciendo la identificación de fortalezas y debilidades, con lo cual se posibilita el diseño de propuestas de mejora a través de procesos planeados de cambio y beneficiando el desarrollo de habilidades hacia la producción y comunicación científica. Abstract: The present research exposes a set of standards composed of different dimensions and performance indicators to evaluate the competence in scientific communication in Mexican university professors. The study consisted of different complementary and subsequent phases: (i) documentary research on normative and theoretical elements that support the initial identification of performance indicators for scientific communication evaluation; (ii) validation of information by 32 expert researchers in science; (iii) validation of information by 62 experts in information literacy (IL); and (iv) derivation of a set of standards, which were tested by 28 university professors in the area of chemical sciences with scientific potential. The results of the research defined a set of standards made up of eight dimensions and 34 performance indicators, to later test their functionality by diagnosing individual and collective levels of competence in scientific communication, favoring the identification of strengths and weaknesses, thereby enabling the design of improvement proposals through planned processes of change and benefiting the development of skills towards scientific production and communication.

Mithramycin A is an antitumor compound used for treatment of several types of cancer including chronic and acute myeloid leukemia, testicular carcinoma, hypercalcemia and Paget's disease. Selective modifications of this molecule by combinatorial biosynthesis and biocatalysis opened the possibility to produce mithramycin analogues with improved properties that are currently under preclinical development. The mithramycin A biosynthetic gene cluster from Streptomyces argillaceus ATCC12956 was cloned by transformation assisted recombination in Saccharomyces cerevisiae and heterologous expression in Streptomyces lividans TK24 was evaluated. Mithramycin A was efficiently produced by S. lividans TK24 under standard fermentation conditions. To improve the yield of heterologously produced mithramycin A, a collection of derivative strains of S. lividans TK24 were constructed by sequential deletion of known potentially interfering secondary metabolite gene clusters using a protocol based on the positive selection of double crossover events with blue pigment indigoidine-producing gene. Mithramycin A production was evaluated in these S. lividans strains and substantially improved mithramycin A production was observed depending on the deleted gene clusters. A collection of S. lividans strains suitable for heterologous expression of actinomycetes secondary metabolites were generated and efficient production of mithramycin A with yields close to 3 g/L, under the tested fermentation conditions was achieved using these optimized collection of strains.

This paper presents an unusual topology of a medium-power seven-level inverter that utilizes a single dc source and a three-phase transformer to generate high-performance seven-level voltage waveforms without complex cascade H-bridges with isolated dc supplies or neutral-point-clamped circuits with capacitor balancing techniques. In contrast to typical topologies of multilevel inverters, the control strategy of the presented circuit facilitates its implementation on a simple 16-bit microcontroller, such that the proposed inverter is operated under a space vector mode. The principle of operation of the seven-level inverter is analyzed, using idealized waveforms for easy and straight implementation together with a description of its practical development, showing experimental results obtained with a 1-kW prototype.

This work corresponds to a practical and transversal integration process of Information Literacy in university curricula, specifically with undergraduate students from the Philosophy program of the Autonomous University of Chihuahua (Mexico), by developing alternatives to evolve traditional classroomteaching practices toward integrating Learning Communities and using Action Research as means ofinfluencing a continuous improvement upon learning processes. This chapter discusses basic concepts from this study and provides the results, which were a product of the data collected from ethnographicprocesses. This practical experience has demonstrated the feasibility of combining this study’scomponents for the achievement of active learning, but also for identifying specific elements that inhibita full implementation.

Ministry of Economy, This work was supported by grants to CM from the Spanish Ministry of Economy and Competitiveness, MINECO (Grants BIO2011-25398, BIO2014-56752-R and PIM2010EEI-00752) and “Apoyo a grupos de excelencia,” Principado de Asturias-FEDER (FC-15-GRUPIN14-014). EntreChem SL acknowledges funding to the ERA-IB program and MINECO (PIM2010EEI-00752). SY and DZ were recipient of predoctoral fellowships from MINECO. We thank Fundación Bancaria Cajastur for financial support to CO, and we also thank Dr. Fernando Reyes from Fundación Medina, and Dr. Javier González-Sabín and Dr. Nicolás Ríos-Lombardía from Entrechem S.L. for technical support in structural elucidation compounds.

This work, including the efforts of Carmen Méndez, was funded by Ministerio de Economía y Competitividad (This work, including the efforts of Carmen Mendez, was funded by Ministerio de Economía y Competitividad (MINECO) (PCIN-2014-066). This work, including the efforts of Francisco Morris, was funded by Ministerio de Economía y Competitividad (MINECO) (PCIN-2014-097). This work, including the efforts of Harald Gross and Pierre Koch, was funded by Bundesministerium für Bildung und Forschung (BMBF) (FKZ 031A568A). This work, including the efforts of Wolfgang Wohlleben, was funded by Bundesministerium für Bildung und Forschung (BMBF) (FKZ 031A568B). This work, including the efforts of Jolanta Zakrzewska-Czerwinska, was funded by MNiSW | Narodowe Centrum Badani Rozwoju (NCBR) (ERA-NET-IB/NeBrasCa/10/2015).). This work, including the efforts of Francisco Morris, was funded by Ministerio de Economía y Competitividad (MINECO) (PCIN-2014-097). This work, including the efforts of Harald Gross and Pierre Koch, was funded by Bundesministerium für Bildung und Forschung (BMBF) (FKZ 031A568A). This work, including the efforts of Wolfgang Wohlleben, was funded by Bundesministerium für Bildung und Forschung (BMBF) (FKZ 031A568B). This work, including the efforts of Jolanta Zakrzewska-Czerwinska, was funded by MNiSW | Narodowe Centrum Badan´ i Rozwoju (NCBR) (ERA-NET-IB/NeBrasCa/10/2015).

Rett syndrome (RTT) is a severe neurodevelopmental disorder caused by mutations in the X chromosomal gene Methyl-CpG-binding Protein 2 (MECP2) (1). RTT treatment so far is symptomatic. Mecp2 disruption in mice phenocopies major features of the syndrome (2) that can be reversed upon re-expression of Mecp2 (3. It has recently been reported that transplantation of wild type (WT) bone marrow (BMT) into lethally irradiated Mecp2tm1.1Jae/y mice prevented neurologic decline and early death by restoring microglial phagocytic activity against apoptotic targets (4). Based on this report, clinical trials of BMT for patients with RTT have been initiated (5). We aimed to replicate and extend the BMT experiments in three different RTT mouse models but found that despite robust microglial engraftment, BMT from WT donors did not rescue early death or ameliorate neurologic deficits. Furthermore, early and specific genetic expression of Mecp2 in microglia did not rescue Mecp2-deficient mice. In conclusion our experiments do not support BMT as therapy for RTT.

Autoantibodies against nucleolar antigens are common in systemic sclerosis (SSc). They include autoantibodies against fibrillarin (Fb), which are serological markers for SSc. Fb is associated with the evolutionally-conserved box C/D of small nucleolar RNAs (snoRNAs). We compared indirect immunofluorescence (IIF), Western blot (WB), and immunoprecipitation (IPP) of total small RNAs assays to determine which of these techniques is most specific for the detection of snoRNPs. We also examined the frequency and specificity of autoantibodies from SSc patients to snoRNAs, snRNAs, and scRNAs, and concluded that 1) IIF can not determine autoantibody specificity against Fb, 2) 36% of SSc sera were false-negative by WB, and 3) by IPP, anti-Fb autoantibodies from SSc patients can bind U3, U8, U13, U15, and U22 snoRNAs.

Sequence comparisons of multiple acyltransferase (AT) domains from modular polyketide synthases (PKSs) have highlighted a correlation between a short sequence motif and the nature of the extender unit selected. When this motif was specifically altered in the bimodular model PKS DEBS1-TE of Saccharopolyspora erythraea, the products included triketide lactones in which acetate extension units had been incorporated instead of propionate units at the predicted positions. We also describe a cassette system for convenient construction of hybrid modular PKSs based on the tylosin PKS in Streptomyces fradiae and demonstrate its use in domain and module swaps.

The soluble, diffusible red-brown pigment produced by a Saccharopolyspora erythraea "red variant" has been shown to contain glycosylated and polymerized derivatives of 2,5,7-trihydroxy-1,4-naphthoquinone (flaviolin). Flaviolin is a spontaneous oxidation product of 1,3,6,8-tetrahydroxynaphthalene (THN), which is biosynthesized in bacteria by a chalcone synthase-like (CS-like) type III polyketide synthase (PKS). A fragment of the gene responsible for THN biosynthesis in S. erythraea E_8-7 was amplified by polymerase chain reaction (PCR) using degenerate primers based on conserved regions of known plant CS and bacterial CS-like genes. From the isolated fragment, a suicide vector was prepared, which was subsequently used to disrupt the red-brown pigment-producing (rpp) locus in S. erythraea, generating a mutant that displayed an albino phenotype. Chromosomal DNA from the albino mutant was subsequently used in a vector-recapture protocol to isolate a plasmid that contained an insert spanning the entire rpp locus. Sequencing of the insert revealed that the disrupted open reading frame (ORF) encodes a CS-like protein displaying 69% sequence identity to the rppA gene of Streptomyces griseus. The S. griseus rppA gene encodes RppA, the first characterized bacterial CS-like protein, which is sufficient in vitro for the synthesis of THN from malonyl-CoA. The rppA disruption mutant and rppA sequence provided a means by which to address the mechanism of diffusible pigment biosynthesis, as well as to investigate any link between this and the modulation of erythromycin A titre, which has been observed for S. erythraea variants.

Chain initiation on many modular polyketide synthases is mediated by acyl transfer from the CoA ester of a dicarboxylic acid, followed by decarboxylation in situ by KSQ, a ketosynthase-like decarboxylase domain. Consistent with this, the acyltransferase (AT) domains of all KSQ-containing loading modules are shown here to contain a key arginine residue at their active site. Site-specific replacement of this arginine residue in the oleandomycin (ole) loading AT domain effectively abolished AT activity, consistent with its importance for catalysis. Substitution of the ole PKS loading module, or of the tylosin PKS loading module, for the erythromycin (ery) loading module gave polyketide products almost wholly either acetate derived or propionate derived, respectively, instead of the mixture found normally. An authentic extension module AT domain, rap AT2 from the rapamycin PKS, functioned appropriately when engineered in the place of the ole loading AT domain, and gave rise to substantial amounts of C13-methylerythromycins, as predicted. The role of direct acylation of the ketosynthase domain of ex-tension module 1 in chain initiation was confirmed by demonstrating that a mutant of the triketide synthase DEBS1-TE, in which the 4'-phosphopante-theine attachment site for starter acyl groups was specifically removed, produced triketide lactone pro-ducts in detectable amounts.

Background: The 6-deoxyerythronolide B synthase (DEBS) of Saccharopolyspora erythraea , which synthesizes the aglycone core of the antibiotic erythromycin A, contains some 30 active sites distributed between three multienzyme polypeptides (designated DEBS1–3). This complexity has hitherto frustrated mechanistic analysis of such enzymes. We previously produced a mutant strain of S. erythraea in which the chain-terminating cyclase domain (TE) is fused to the carboxyl-terminus of DEBS1, the multienzyme that catalyzes the first two rounds of polyketide chain extension in S. erythraea . This mutant strain produces triketide lactone in vivo . We set out to purify the chimaeric enzyme and to determine its activity in vitro . Results: The purified DEBS1-TE multienzyme catalyzes synthesis of triketide lactones in vitro . The synthase specifically uses the (2S)-isomer of methylmalonyl-CoA, as previously proposed, but has a more relaxed specificity for the starter unit than in vivo . Conclusions: We have obtained a purified polyketide synthase system, derived from DEBS, which retains catalytic activity. This approach opens the way for mechanistic and structural analyses of active multienzymes derived from any modular polyketide synthase.

The lantibiotic actagardine A is nineteen amino acids in length and comprises three intertwined C-terminal methyllanthionine-bridged rings and an N-terminal lanthionine-bridged ring. Produced by the actinomycete Actinoplanes garbadinensis ATCC 31049, actagardine A demonstrates antibacterial activity against important Gram-positive pathogens. This activity combined with its ribosomal synthesis makes it an attractive target for the generation of lantibiotic variants with improved biological activity. A variant generation system designed to allow the specific substitution of amino acids at targeted sites throughout the actagardine A peptide has been used to generate a comprehensive library by site-directed mutagenesis. With the exception of residues involved in bridge formation, each amino acid in the actagardine A peptide as well as the alanine (ala(0)) at position -1 relative to the mature peptide, has been systematically substituted with all remaining 19 amino acids. A total of 228 mutants have been engineered with 44 produced in good yield. The mutant V15F in particular demonstrates improved activity against a range of notable Gram-positive pathogens including Clostridium difficile, when evaluated alongside actagardine A. The scope of variants generated provides an insight into the flexibility of the actagardine A processing machinery and will undoubtedly assist in future mutational studies.

We have analyzed base pairing interactions between the U5 snRNA and 5' exon sequences during pre-mRNA splicing in a mammalian in vivo system. We constructed synthetic U5 genes with mutations that alter four bases (C3, U4, U5 and U6) within the invariant 9 nt U5 sequence GCCUUUUAC; transient transfection of HeLa cells with these U5 sequences cloned into a U1 expression vector yielded high levels of the mutant snRNAs. To test their function, we cotransfected a rabbit beta-globin gene containing one of two mutations (G1-->A or T2-->A) in the essential GT dinucleotide at the 5' end of the second intron. Certain U5 loop mutants activated novel 5' splice sites only in mutant rabbit beta-globin transcripts. One novel site surprisingly resides in the first exon; its use is invariably coupled to utilization of a particular cryptic 5' splice site in the second exon. All of the newly activated cryptic 5' splice sites exhibit complementarity with the mutant U5 loop in the exon 1-5 nt upstream of the cryptic site, extending previous results in yeast. However, the register of the potential pairing is not identical at the various novel cryptic 5' splice sites, indicating that the interaction between the U5 loop and the 5' exon may be more flexible than previously believed.

Deoxyactagardine B (DAB) is a hitherto unknown type B lantibiotic, produced by Actinoplanes liguriae NCIMB41362. The mature peptide is 19 amino acids in length and structurally analogous to actagardine, differing by two amino acids (V15L and I16V) and the absence of a sulfoxide bond between residues 14 and 19. The biosynthetic genes encoding DAB are clustered, and in addition to the structural gene ligA include genes believed to encode for the proteins responsible for the modification, transport and regulation of DAB synthesis. Surprisingly, despite the presence of a gene that shares significant homology to the monooxygenase garO from the actagardine biosynthetic gene cluster, the oxidized form of DAB has not been detected. A lanA gene encoding the DAB peptide has been introduced into the plasmid pAGvarX and delivered into a strain of Actinoplanes garbadinensis lacking the structural gene for actagardine, garA (A. garbadinensis DeltagarA). Expression of this gene in A. garbadinensis DeltagarA resulted in the production of actagardine B, an oxidized form of DAB.

Summary The biosynthetic pathway of the type B lantibiotic actagardine (formerly gardimycin), produced by Actinoplanes garbadinensis ATCC31049, has been cloned, sequenced and annotated. The gene cluster contains the gene garA that encodes the actagardine prepropeptide, a modification gene garM, involved in the dehydration and cyclization of the prepeptide, several putative transporter and regulatory genes as well as a novel luciferase-like monooxygenase gene designated garO. Expression of these genes in Streptomyces lividans resulted in the production of ala(0)-actagardine while deletion of the garA gene from A. garbadinensis generated a strain incapable of producing actagardine. Actagardine production was successfully restored however, by the delivery of the plasmid pAGvarX. This plasmid contains an engineered cassette of the actagardine encoding gene garA and offers an alternative route to generating extensive libraries of actagardine variants. Using this plasmid, an alanine scanning library has been constructed and the mutants analysed. Further modifications include the removal of the novel garO gene from A. garbadinensis. Deletion of this gene resulted in the production of deoxy variants of actagardine, demonstrating that the formation of the sulfoxide group is enzyme catalysed and not a spontaneous chemical modification as previously believed.

Summary Mersacidin is a tetracyclic lantibiotic with antibacterial activity against Gram-positive pathogens. To probe the specificity of the biosynthetic pathway of mersacidin and obtain analogs with improved antibacterial activity, an efficient system for generating variants of this lantibiotic was developed. A saturation mutagenesis library of the residues of mersacidin not involved in cycle formation was constructed and used to validate this system. Mersacidin analogs were obtained in good yield in approximately 35% of the cases, producing a collection of 82 new compounds. This system was also used for the production of deletion and insertion mutants of mersacidin. The outcome of these studies suggests that this system can be extended to produce mersacidin variants with multiple changes that will allow a full investigation of the potential use of modified mersacidins as therapeutic agents.

Resumen:El presente documento expone los resultados de una investigación enfocada en la búsqueda de teorías que den sustento a lo que deberá ser un modelo para evaluar la participación institucional en el desarrollo de las competencias informacionales del estudiantado. La investigación se basa principalmente en revisión de la literatura y en las reflexiones que las lecturas inspiraron. Los resultados llevan a las personas autoras a concluir que un modelo de evaluación puede enmarcarse en la Teoría General de Sistemas en cuanto a la transformación que se espera lograr en estudiantes durante su paso por la universidad, pero que para lograr una visión más completa se requiere identificar una teoría del aprendizaje; se encuentra que la que puede brindar mayores explicaciones es la recientemente desarrollada Teoría del Conectivismo, como una forma de expansión de las teorías constructivistas del aprendizaje. Abstract:This document presents the results of a study focused on the search for theories to support what should be an evaluation model of university efforts aimed to develop student's information competencies. The research is mainly based on literature review and on the reflections that the readings inspired. The results lead the authors to conclude that an evaluation model can be framed in the General Systems Theory as to the transformation to be achieved by students during their pass by the university; nevertheless, for a more complete picture, it is necessary to identify a learning theory: we observe that one that may provide further explanations is the recently developed theory of Connectivism, as a way of expanding constructivist theories of learning.

Autoantibodies against nucleolar antigens are common in systemic sclerosis (SSc). They include autoantibodies against fibrillarin (Fb), which are serological markers for SSc. Fb is associated with the evolutionally‐conserved box C/D of small nucleolar RNAs (snoRNAs). We compared indirect immunofluorescence (IIF), Western blot (WB), and immunoprecipitation (IPP) of total small RNAs assays to determine which of these techniques is most specific for the detection of snoRNPs. We also examined the frequency and specificity of autoantibodies from SSc patients to snoRNAs, snRNAs, and scRNAs, and concluded that 1) IIF can not determine autoantibody specificity against Fb, 2) 36% of SSc sera were false‐negative by WB, and 3) by IPP, anti‐Fb autoantibodies from SSc patients can bind U3, U8, U13, U15, and U22 snoRNAs. J. Clin. Lab. Anal. 18:19–26, 2004. © 2004 Wiley‐Liss, Inc.

Macrocyclic polyketides exhibit an impressive range of medically useful activities, and there is great interest in manipulating the genes that govern their synthesis. The 6-deoxyerythronolide B synthase (DEBS) of Saccharopolyspora erythraea, which synthesizes the aglycone core of the antibiotic erythromycin A, has been modified by repositioning of a chain-terminating cyclase domain to the carboxyl-terminus of DEBS1, the multienzyme that catalyzes the first two rounds of polyketide chain extension. The resulting mutant markedly accelerates formation of the predicted triketide lactone, compared to a control in which the repositioned domain is inactive. Repositioning of the cyclase should be generally useful for redirecting polyketide synthesis to obtain polyketides of specified chain lengths.

The CACNA1C gene encoding the Cav1.2 subunit of the L-type calcium channel has emerged as a new candidate gene for neuropsychiatric disease, including bipolar disorder, major depression, schizophrenia and autism.1, 2, 3 We report that global haploinsufficiency, forebrain-specific elimination and prefrontal cortex (PFC)-specific knockdown of cacna1c all increase anxiety-related behavior in mice, a prominent component of the forms of neuropsychiatric disease in which aberrations in CACNA1C have been implicated, without affecting compulsive behavior. Constitutive cacna1c heterozygous mice (HET) were evaluated in three behavioral assays related to anxiety: open field test, light–dark conflict test and elevated plus maze (EPM). HETs displayed anxiety-like behavior in the EPM (Figure 1a), spending significantly less time exploring the open arms compared with wild-type littermate controls (WT; F1,19=6.437; P

The biosynthesis of complex reduced polyketides is catalysed in actinomycetes by large multifunctional enzymes, the modular Type I polyketide synthases (PKSs). Most of our current knowledge of such systems stems from the study of a restricted number of macrolide-synthesising enzymes. The sequencing of the genes for the biosynthesis of monensin A, a typical polyether ionophore polyketide, provided the first genetic evidence for the mechanism of oxidative cyclisation through which polyethers such as monensin are formed from the uncyclised products of the PKS. Two intriguing genes associated with the monensin PKS cluster code for proteins, which show strong homology with enzymes that trigger double bond migrations in steroid biosynthesis by generation of an extended enolate of an unsaturated ketone residue. A similar mechanism operating at the stage of an enoyl ester intermediate during chain extension on a PKS could allow isomerisation of an E double bond to the Z isomer. This process, together with epoxidations and cyclisations, form the basis of a revised proposal for monensin formation. The monensin PKS has also provided fresh insight into general features of catalysis by modular PKSs, in particular into the mechanism of chain initiation.

Antibiotic-producing polyketide synthases (PKSs) are enzymes responsible for the biosynthesis in Streptomyces and related filamentous bacteria of a remarkably broad range of bioactive metabolites, including antitumour aromatic compounds such as mithramycin and macrolide antibiotics such as erythromycin. The molecular basis for the selection of the starter unit on aromatic PKSs is unknown. Here we show that a component of aromatic PKS, previously named 'chain-length factor', is a factor required for polyketide chain initiation and that this factor has decarboxylase activity towards malonyl-ACP (acyl carrier protein). We have re-examined the mechanism of initiation on modular PKSs and have identified as a specific initiation factor a domain of previously unknown function named KSQ, which operates like chain-length factor. Both KSQ and chain-length factor are similar to the ketosynthase domains that catalyse polyketide chain extension in modular multifunctional PKSs and in aromatic PKSs, respectively, except that the ketosynthase domain active-site cysteine residue is replaced by a highly conserved glutamine in KSQ and in chain-length factor. The glutamine residue is important both for decarboxylase activity and for polyketide synthesis.

Background: Polyketides are structurally diverse natural products that have a range of medically useful activities. Nonaromatic bacterial polyketides are synthesised on modular polyketide synthase (PKS) multienzymes, in which each cycle of chain extension requires a different ‘module' of enzymatic activities. Attempts to design and construct modular PKSs that synthesise specified novel polyketides provide a particularly stringent test of our understanding of PKS structure and function. Results: We have constructed bimodular and trimodular PKSs based on DEBS1-TE, a derivative of the erythromycin PKS that contains only modules 1 and 2 and a thioesterase (TE), by substituting multiple domains with appropriate counterparts derived from the rapamycin PKS. Hybrid PKSs were obtained that synthesised the predicted target triketide lactones, which are simple analogues of cholesterol-lowering statins. In constructing intermodular fusions, whether between modules in the same or in different proteins, it was found advantageous to preserve intact the acyl carrier protein-ketosynthase (ACP-KS) didomain that spans the junction between successive modules. Conclusions: Relatively simple considerations govern the construction of functional hybrid PKSs. Fusion sites should be chosen either in the surface-accessible linker regions between enzymatic domains, as previously revealed, or just inside the conserved margins of domains. The interaction of an ACP domain with the adjacent KS domain, whether on the same polyketide or not, is of particular importance, both through conservation of appropriate protein-protein interactions, and through optimising molecular recognition of the altered polyketide chain in the key transfer of the acyl chain from the ACP of one module to the KS of the downstream module.

Background Polyketides are compounds that possess medically significant activities. The modular nature of the polyketide synthase (PKS) multienzymes has generated interest in bioengineering new PKSs. Rational design of novel PKSs, however, requires a greater understanding of the stereocontrol mechanisms that operate in natural PKS modules. Results The N -acetyl cysteamine (NAC) thioester derivative of the natural β-keto diketide intermediate was incubated with DEBS1-TE, a derivative of the erythromycin PKS that contains only modules 1 and 2. The reduction products of the two ketoreductase (KR) domains of DEBS1 -TE were a mixture of the (2S.3 R ) and (2 R ,3 S ) isomers of the corresponding β-hydroxy diketide NAC thioesters. Repeating the incubation using a DEBS1-TE mutant that only contains KR1 produced only the (2 S ,3 R ) isomer. Conclusions In contrast with earlier results, KR1 selects only the (2 S ) isomer and reduces it stereospecifically to the (2S,3 R )-3-hydroxy-2-methyl acyl product. The KR domain of module 1 controls the stereochemical outcome at both methyland hydroxyl-bearing chiral centres in the hydroxy diketide intermediate. Earlier work showed that the normal enzyme-bound ketoester generated in module 2 is not epimerised, however. The stereochemistry at C-2 is therefore established by a condensation reaction that exclusively gives the (2 R )-ketoester, and the stereochemistry at C-3 by reduction of the keto group. Two different mechanisms of stereochemical control, therefore, operate in modules 1 and 2 of the erythromycin PKS. These results should provide a more rational basis for designing hybrid PKSs to generate altered stereochemistry in polyketide products.

ERYTHROMYCIN A, a clinically important polyketide antibiotic, is produced by the Gram-positive bacterium Saccharopolyspora erythraea.. In an arrangement that seems to be generally true of antibiotic biosynthetic genes in Streptomyces and related bacteria like S. erythraea1, the ery genes encoding the biosynthetic pathway to erythromvein are clustered around the gene (ermE) that confers self-resistance on S. erythraea2–6. The aglycone core of erythro-mycin A is derived from one propionyl-CoA and six methylmalonyl-CoA units, which are incorporated head-to-tail7–10 into the growing polyketide chain, in a process similar to that of fatty-acid biosynthesis1, to generate a macrolide intermediate, 6-deoxyeryth-ronolide B10. 6-Deoxyerythronolide B is converted into erythro-mycin A through the action2–5,10 of specific hydroxylases, glycosyItransferases and a methyltransferase. We report here the analysis of about 10 kilobases of DNA from S. erythraea, cloned by chromosome 'walking' outwards from the erythromycin-resistance determinant ermE, and previously shown to be essential for erythromycin biosynthesis5,11. Partial sequencing of this region12 indicates that it encodes the synthase. Our results confirm this, and reveal a novel organization of the erythromycin-producing polyketide synthase, which provides further insight into the mechanism of chain assembly.

A new integrative vector (pCJR24) was constructed for use in the erythromycin producer Saccharopolyspora erythraea and in other actinomycetes. It includes the pathway-specific activator gene actII–ORF4 from the actinorhodin biosynthetic gene cluster of Streptomyces coelicolor. The actI promoter and the associated ribosome binding site are located upstream of an NdeI site (5′-CATATG-3′) which encompasses the actI start codon allowing protein(s) to be produced at high levels in response to nutritional signals if these signals are faithfully mediated by the ActII–ORF4 activator. Several polyketide synthase genes were cloned in pCJR24 and overexpressed in S. erythraea after integration of the vector into the chromosome by homologous recombination, indicating the possibility that the S. coelicolor promoter/activator functions appropriately in S. erythraea. pCJR24-mediated recombination was also used to place the entire gene set for the erythromycin-producing polyketide synthase under the control of the actI promoter. The resulting strain produced copious quantities of erythromycins and precursor macrolides when compared with wild-type S. erythraea. The use of this system provides the means for rational strain improvement of antibiotic-producing actinomycetes.