Search

PPR proteins are a family of ubiquitous RNA-binding factors, found in all the Eukaryotic lineages, and are particularly numerous in higher plants. According to recent bioinformatic analyses, yeast genomes encode from 10 (in S. pombe) to 15 (in S. cerevisiae) PPR proteins. All of these proteins are mitochondrial and very often interact with the mitochondrial membrane. Apart from the general factors, RNA polymerase and RNase P, most yeast PPR proteins are involved in the stability and/or translation of mitochondrially encoded RNAs. At present, some information concerning the target RNA(s) of most of these proteins is available, the next challenge will be to refine our understanding of the function of the proteins and to resolve the yeast PPR-RNA-binding code, which might differ significantly from the plant PPR code.

Like all ciliates, Paramecium tetraurelia is a unicellular eukaryote that harbors two kinds of nuclei within its cytoplasm. At each sexual cycle, a new somatic macronucleus (MAC) develops from the germ line micronucleus (MIC) through a sequence of complex events, which includes meiosis, karyogamy, and assembly of the MAC genome from MIC sequences. The latter process involves developmentally programmed genome rearrangements controlled by noncoding RNAs and a specialized RNA interference machinery. We describe our first attempts to identify genes and biological processes that contribute to the progression of the sexual cycle. Given the high percentage of unknown genes annotated in the P. tetraurelia genome, we applied a global strategy to monitor gene expression profiles during autogamy, a self-fertilization process. We focused this pilot study on the genes carried by the largest somatic chromosome and designed dedicated DNA arrays covering 484 genes from this chromosome (1.2% of all genes annotated in the genome). Transcriptome analysis revealed four major patterns of gene expression, including two successive waves of gene induction. Functional analysis of 15 upregulated genes revealed four that are essential for vegetative growth, one of which is involved in the maintenance of MAC integrity and another in cell division or membrane trafficking. Two additional genes, encoding a MIC-specific protein and a putative RNA helicase localizing to the old and then to the new MAC, are specifically required during sexual processes. Our work provides a proof of principle that genes essential for meiosis and nuclear reorganization can be uncovered following genome-wide transcriptome analysis.

ABSTRACTLike all ciliates, Paramecium tetraureliais a unicellular eukaryote that harbors two kinds of nuclei within its cytoplasm. At each sexual cycle, a new somatic macronucleus (MAC) develops from the germ line micronucleus (MIC) through a sequence of complex events, which includes meiosis, karyogamy, and assembly of the MAC genome from MIC sequences. The latter process involves developmentally programmed genome rearrangements controlled by noncoding RNAs and a specialized RNA interference machinery. We describe our first attempts to identify genes and biological processes that contribute to the progression of the sexual cycle. Given the high percentage of unknown genes annotated in the P. tetraureliagenome, we applied a global strategy to monitor gene expression profiles during autogamy, a self-fertilization process. We focused this pilot study on the genes carried by the largest somatic chromosome and designed dedicated DNA arrays covering 484 genes from this chromosome (1.2% of all genes annotated in the genome). Transcriptome analysis revealed four major patterns of gene expression, including two successive waves of gene induction. Functional analysis of 15 upregulated genes revealed four that are essential for vegetative growth, one of which is involved in the maintenance of MAC integrity and another in cell division or membrane trafficking. Two additional genes, encoding a MIC-specific protein and a putative RNA helicase localizing to the old and then to the new MAC, are specifically required during sexual processes. Our work provides a proof of principle that genes essential for meiosis and nuclear reorganization can be uncovered following genome-wide transcriptome analysis.

Reaction of imidoyl chlorides ArN=CClR Ar = 2iPrC6H4, 2,6iPr2C6H3, 2MeOC6H4; R = Me, Ph, tBu with [Linacnac] [nacnac = ArNCMe2CH] gives βtriketimines L, most of which exist in solution in equilibrium with their imineenamine tautomers. The route is highly modular, allowing independent variation of at least five parameters. The solution equilibria are very sensitive to such substituent pattern variation. Singlecrystal Xray diffraction analyses of examples of both tautomers and a geometric isomer in the solid state are presented, alongside solution NMR studies of the tautomerism. All examples revert exclusively to the βtriimine form on complexation with MCO3fragments M = Cr, Mo, W. Facial isomers result. The ligands are weak σdonors, as adjudged by CO IR stretching frequencies in [LMCO3]. Crystalstructure determination on the isostructural pair [HC2iPrC6H4N=CMe3MCO3] M = Cr, Mo revealed a hexagonal packing arrangement composed of aryl–aryl and carbonyl CO–H–C interactions which generates pseudocylindrical voids accounting for 6–9  of the crystal volume. In only one case were these occupied by solvent molecules. This family of facially capping N,N,Nligands with finely tunable bulk have wide potential in coordination chemistry.© WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009

The APHgene of a butirosin‐producing Bacillus circulanshas been cloned and sequenced; a comparison of the translated protein sequence with those from TN5 and TN903 indicates that they may have a common origin.

The APHgene of a butirosin-producing Bacillus circulanshas been cloned and sequenced; a comparison of the translated protein sequence with those from TN5 and TN903 indicates that they may have a common origin.

We have deleted the yeast gene YJR025cand shown that this leads to an auxotrophy for nicotinic acid. The deduced protein sequence of the gene product is homologous to the human 3-hydroxyanthranilic acid dioxygenase (EC 1.13.11.6) which is part of the kynurenine pathway for the degradation of tryptophan and the biosynthesis of nicotinic acid. In cell-free extracts the 3-hydroxyanthranilic acid dioxygenase activity is proportional to the copy number of the YJR025cgene. As YJR025cencodes the yeast 3-hydroxyanthranilic acid dioxygenase, we have named this gene BNA1for biosynthesis of nicotinic acid.

We have deleted the yeast gene YJR025cand shown that this leads to an auxotrophy for nicotinic acid. The deduced protein sequence of the gene product is homologous to the human 3‐hydroxyanthranilic acid dioxygenase (EC 1.13.11.6) which is part of the kynurenine pathway for the degradation of tryptophan and the biosynthesis of nicotinic acid. In cell‐free extracts the 3‐hydroxyanthranilic acid dioxygenase activity is proportional to the copy number of the YJR025cgene. As YJR025cencodes the yeast 3‐hydroxyanthranilic acid dioxygenase, we have named this gene BNA1for iosynthesis of icotinic cid.

We studied the NAM2 genes of Saccharomyces douglasii and Saccharomyces cerevisiae, and showed that they are interchangeable for all the known functions of these genes, both mitochondrial protein synthesis and mitochondrial mRNA splicing. This confirms the prediction that the S. douglasii NAM2D gene encodes the mitochondrial leucyl tRNA synthetase (EC 6.1.1.4). The observation that these enzymes are interchangeable for their mRNA splicing functions, even though there are significant differences in the intron/exon structure of their mitochondrial genome, suggests that they may have a general role in yeast mitochondrial RNA splicing. A short open reading frame (ORF) precedes the synthetase-encoding ORF, and we showed that at least in S. cerevisiae this is not essential for the expression of the gene; however, it may be involved in a more subtle type of regulation. Sequence comparisons of S. douglasii and S. cerevisiae revealed a particularly interesting situation from the evolutionary point of view. It appears that the two yeasts have diverged relatively recently: there is remarkable nucleotide sequence conservation, with no deletions or insertions, but numerous (albeit non-saturating) silent substitutions resulting from transitions. This applies not only to the NAM2 coding regions, but also to two other ORFs flanking the NAM2 ORF. The regions between the ORFs (believed to be intergenic regions) are much less conserved, with several deletions and insertions. Thus S. douglasii and S. cerevisiae provide an ideal system for the study of molecular evolution, being two yeasts “caught in the act” of speciation.

mna2, which belongs to the class I temperature-sensitive pet mutants that lose mitochondrial (mt)RNA at restrictive temperature, was shown by complementation and sequence determination to correspond to the gene coding for HSP60. Both mna2-1 and mna2-2, the two available alleles of mna2, have conservative single amino acid substitutions in the HSP60 gene. Valine substitutes for an alanine (position 47) in mna2-1, and an isoleucine substitutes for a valine (position 77) in mna2-2. These substitutions result in defects in respiration and in steady-state mtRNA accumulation. Wild-type hsp60 alleviates the mtRNA phenotype completely, while partially relieving the respiratory deficiency.

The mitochondrial leucyl-tRNA synthetase (mLRS) of Saccharomyces cerevisiae is involved in both mitochondrial protein synthesis and pre-mRNA splicing. We have created mutations in the regions HIGH, GWD and KMSKS, which are involved in ATP-, amino acid-and tRNA-binding respectively, and which have been conserved in the evolution of group I tRNA synthetases. The mutants GRD and NMSKS have no discernible phenotype. The mutants AWD and ARD act as null alleles and lead to the production of 100% cytoplasmic petites. The mutants HIGN, NIGH and KMSNS are unable to grown on glycerol even in the presence of an intronless mitochondrial genome and accumulate petites to a greater extent than the wild-type but less than 40%. Experiments with an imported bI4 maturase indicate that the lesion in these mutations primarily affects the synthetase and not the splicing functions.

We present observations of optical power limiting using a thermal nonlinearity in a dye-doped colloidal crystal. The transmission of the crystal is studied as a function of the incident intensity for various dye concentrations, lattice spacings, and wavelengths. We have found that optical limiting occurs when the wavelength of the incident light is tuned to the blue edge of the stop gap of these structures. Limiting intensities near 10 kW/cm^2 have been obtained for colloidal solutions with 10^−5 M Kiton Red dye. The experimental results are compared with theoretical models of nonlinear distributive-feedback structures in which the nonlinearity is assumed to be thermal.

Optical switching and optical bistability and multistability are observed experimentally with a nonlinear periodic structure. The periodic dielectric is a colloidal crystal that exhibits a large electrostrictive nonlinearity. The transmission characteristics of these crystals as a function of incident intensity are presented for several different frequencies of light within the stopgap of the periodic structures.

OligoArray is a program that computes gene specific and secondary structure free oligonucleotides for genome-scale oligonucleotide microarray construction or other applications.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.