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Flow cytometry (FCM) is a high‐throughput fluorescence‐based technique for multiparameter analysis of individual particles, including cells and nanoparticles. Currently, however, FCM does in many cases not permit proper counting of fluorophore‐tagged markers on individual particles, due to a lack of tools for translating FCM output intensities into accurate numbers of fluorophores. This lack hinders derivation of detailed biologic information and comparison of data between experiments with FCM. To address this technological void, the authors here use DNA nanotechnology to design and construct barrel‐shaped DNA‐origami nanobeads for fluorescence/antigen quantification in FCM. Each bead contains a specific number of calibrator fluorophores and a fluorescent trigger domain with an alternative fluorophore for proper detection in FCM. Using electron microscopy, single‐particle fluorescence microscopy, and FCM, the design of each particle is verified. To validate that the DNA bead‐based FCM calibration enabled the authors to determine the number of antigens on a biological particle, the uniform and well‐characterized murine leukemia virus (MLV) is studied. 48 ± 11 envelope surface protein (Env) trimers per MLV is obtained, which is consistent with reported numbers that relied on low‐throughput imaging. Thus, the authors' DNA‐beads should accelerate quantitative studies of the biology of individual particles with FCM. [ABSTRACT FROM AUTHOR]

With the novel possibilities for detecting molecules of interest with extreme sensitivity also comes the risk of encountering hitherto negligible sources of error. In life science, such sources of error might be the broad variety of additives such as dithiothreitol (DTT) used to preserve enzyme stability during in vitro reactions. Using two different assays that can sense strand interruptions in double stranded DNA, we here show that DTT is able to introduce nicks in the DNA backbone. DTT was furthermore shown to facilitate the immobilization of fluorescent DNA on an NHS-ester functionalized glass surface. Such reactions may in particular impact the readout from single molecule detection studies and other ultrasensitive assays. This was highlighted by the finding that DTT markedly decreased the signal to noise ratio in a DNA sensor based assay with single molecule resolution. [ABSTRACT FROM AUTHOR]

Several studies have shown that human endogenous retroviruses and endogenous retrovirus-like repeats (here collectively HERVs) impose direct regulation on human genes through enhancer and promoter motifs present in their long terminal repeats ( LTRs). Although chimeric transcription in which novel gene isoforms containing retroviral and human sequence are transcribed from viral promoters are commonly associated with disease, regulation by HERVs is beneficial in other settings; for example, in human testis chimeric isoforms of TP63 induced by an ERV9 LTR protect the male germ line upon DNA damage by inducing apoptosis, whereas in the human globin locus the γ- and β-globin switch during normal hematopoiesis is mediated by complex interactions of an ERV9 LTR and surrounding human sequence. The advent of deep sequencing or next-generation sequencing (NGS) has revolutionized the way researchers solve important scientific questions and develop novel hypotheses in relation to human genome regulation. We recently applied next-generation paired-end RNA-sequencing (RNA-seq) together with chromatin immunoprecipitation with sequencing (ChIP-seq) to examine ERV9 chimeric transcription in human reference cell lines from Encyclopedia of DNA Elements (ENCODE). This led to the discovery of advanced regulation mechanisms by ERV9s and other HERVs across numerous human loci including transcription of large gene-unannotated genomic regions, as well as cooperative regulation by multiple HERVs and non-LTR repeats such as Alu elements. In this article, well-established examples of human gene regulation by HERVs are reviewed followed by a description of paired-end RNA-seq, and its application in identifying chimeric transcription genome-widely. Based on integrative analyses of RNA-seq and ChIP-seq, data we then present novel examples of regulation by ERV9s of tumor suppressor genes CADM2 and SEMA3A, as well as transcription of an unannotated region. Taken together, this article highlights the high suitability of contemporary sequencing methods in future analyses of human biology in relation to evolutionary acquired retroviruses in the human genome. [ABSTRACT FROM AUTHOR]

Rapid and reliable diagnosis is essential in the fight against malaria, which remains one of the most deadly infectious diseases in the world. In the present study we take advantage of a droplet microfluidics platform combined with a novel and user-friendly biosensor for revealing the main malaria-causing agent, the Plasmodium falciparum (P. falciparum) parasite. Detection of the parasite is achieved through detection of the activity of a parasite-produced DNA-modifying enzyme, topoisomerase I (pfTopoI), in the blood from malaria patients. The assay presented has three steps: (1) droplet microfluidics-enabled extraction of active pfTopoI from a patient blood sample; (2) pfTopoI-mediated modification of a specialized DNA biosensor; (3) readout. The setup is quantitative and specific for the detection of Plasmodium topoisomerase I. The procedure is a considerable improvement of the previously published Rolling Circle Enhanced Enzyme Activity Detection (REEAD) due to the advantages of involving no signal amplification steps combined with a user-friendly readout. In combination these alterations represent an important step towards exploiting enzyme activity detection in point-of-care diagnostics of malaria. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) are ~22 base pair-long non-coding RNAs which regulate gene expression in the cytoplasm of eukaryotic cells by binding to specific target regions in mRNAs to mediate transcriptional blocking or mRNA cleavage. Through their fundamental roles in cellular pathways, gene regulation mediated by miRNAs has been shown to be involved in almost all biological phenomena, including development, metabolism, cell cycle, tumor formation, and host-pathogen interactions. To address the latter in a primitive vertebrate host, we here used an array platform to analyze the miRNA response in rainbow trout (Oncorhynchus mykiss) following inoculation with the virulent fish rhabdovirus Viral hemorrhagic septicaemia virus. Two clustered miRNAs, miR-462 and miR-731 (herein referred to as miR-462 cluster), described only in teleost fishes, were found to be strongly upregulated, indicating their involvement in fish-virus interactions. We searched for homologues of the two teleost miRNAs in other vertebrate species and investigated whether findings related to ours have been reported for these homologues. Gene synteny analysis along with gene sequence conservation suggested that the teleost fish miR-462 and miR-731 had evolved from the ancestral miR-191 and miR-425 (herein called miR-191 cluster), respectively. Whereas the miR-462 cluster locus is found between two protein-coding genes (intergenic) in teleost fish genomes, the miR-191 cluster locus is found within an intron of a protein-coding gene (intragenic) in the human genome. Interferon (IFN)-inducible and immune-related promoter elements found upstream of the teleost miR-462 cluster locus suggested roles in immune responses to viral pathogens in fish, while in humans, the miR-191 cluster functionally associated with cell cycle regulation. Stimulation of fish cell cultures with the IFN inducer poly I:C accordingly upregulated the expression of miR-462 and miR-731, while no stimulatory effect on miR-191 and miR-425 expression was observed in human cell lines. Despite high sequence conservation, evolution has thus resulted in different regulation and presumably also different functional roles of these orthologous miRNA clusters in different vertebrate lineages. [ABSTRACT FROM AUTHOR]

Background: Evidence suggests that some human endogenous retroviruses and endogenous retrovirus-like repeats (here collectively ERVs) regulate the expression of neighboring genes in normal and disease states; e.g. the human globin locus is regulated by an ERV9 that coordinates long-range gene switching during hematopoiesis and activates also intergenic transcripts. While complex transcription regulation is associated with integration of certain exogenous retroviruses, comparable regulation sustained by ERVs is less understood. Findings: We analyzed ERV transcription using ERV9 consensus sequences and publically available RNA-sequencing, chromatin immunoprecipitation with sequencing (ChIP-seq) and cap analysis gene expression (CAGE) data from ENCODE. We discovered previously undescribed and advanced transcription regulation mechanisms in several human reference cell lines. We show that regulation by ERVs involves long-ranging activations including complex RNA splicing patterns, and transcription of large unannotated regions ranging in size from several hundred kb to around 1 Mb. Moreover, regulation was found to be cooperatively sustained in some loci by multiple ERVs and also non-LTR repeats. Conclusion: Our analyses show that endogenous retroviruses sustain advanced transcription regulation in human cell lines, which shows similarities to complex insertional mutagenesis effects exerted by exogenous retroviruses. By exposing previously undescribed regulation effects, this study should prove useful for understanding fundamental transcription mechanisms resulting from evolutionary acquisition of retroviral sequence in the human genome. [ABSTRACT FROM AUTHOR]

Background Insertional mutagenesis screens of retrovirus-induced mouse tumors have proven valuable in human cancer research and for understanding adverse effects of retroviral-based gene therapies. In previous studies, the assignment of mouse genes to individual retroviral integration sites has been based on close proximity and expression patterns of annotated genes at target positions in the genome. We here employed next-generation RNA sequencing to map retroviral-mouse chimeric junctions genome-wide, and to identify local patterns of transcription activation in T-lymphomas induced by the murine leukemia gamma-retrovirus SL3-3. Moreover, to determine epigenetic integration preferences underlying long-range gene activation by retroviruses, the colocalization propensity with common epigenetic enhancer markers (H3K4Me1 and H3K27Ac) of 6,117 integrations derived from end-stage tumors of more than 2,000 mice was examined. Results We detected several novel mechanisms of retroviral insertional mutagenesis: bidirectional activation of mouse transcripts on opposite sides of a provirus including transcription of unannotated mouse sequence; sense/antisense-type activation of genes located on opposite DNA strands; tandem-type activation of distal genes that are positioned adjacently on the same DNA strand; activation of genes that are not the direct integration targets; combinationtype insertional mutagenesis, in which enhancer activation, alternative chimeric splicing and retroviral promoter insertion are induced by a single retrovirus. We also show that irrespective of the distance to transcription start sites, the far majority of retroviruses in endstage tumors colocalize with H3K4Me1 and H3K27Ac-enriched regions in murine lymphoid tissues. Conclusions We expose novel retrovirus-induced host transcription activation patterns that reach beyond a single and nearest annotated gene target. Awareness of this previously undescribed layer of complexity may prove important for elucidation of adverse effects in retroviral-based gene therapies. We also show that wild-type gamma-retroviruses are frequently positioned at enhancers, suggesting that integration into regulatory regions is specific and also subject to positive selection for sustaining long-range gene activation in end-stage tumors. Altogether, this study should prove useful for extrapolating adverse outcomes of retroviral vector therapies, and for understanding fundamental cellular regulatory principles and retroviral biology. [ABSTRACT FROM AUTHOR]

To investigate mechanisms and phenotypic effects of insertional mutagenesis by gammaretroviruses, we have developed mouse lines containing a single Akv 1-99 long terminal repeat (LTR) and a floxed PGK/Tn5 neomycin cassette at the Nras proto-oncogene at positions previously identified as viral integration sites in Akv 1-99 induced tumors. The insert did not compromise the embryonic development, however, the cassette had an effect on Nras expression in all tissues analyzed. Cre-mediated excision of the PGK/Tn5 neomycin cassette in two of the lines caused upregulation of Nras. Altogether, the knock-in alleles are characterized by modulation of expression of the target gene from more than ten-fold upregulation to three-fold downregulation and exemplify various mechanisms of deregulation by insertional mutagenesis. LTR knock-in mice may serve as a tool to investigate mechanisms of retroviral insertional mutagenesis and as a way of constitutive or induced modulation of expression of a target gene. [ABSTRACT FROM AUTHOR]

Gene silencing by RNA interference (RNAi) can be achieved by the ectopic expression of tailored short hairpin RNAs (shRNAs) which after export to the cytoplasm are processed by Dicer and incorporated into the RNA induced silencing complex (RISC). Design rules for shRNAs have been the focus of several studies, but only a few reports have turned the attention to the sequence of the loop- region. In this work we selected high-functional and low-functional shRNA loops from retroviral hairpin-loop-libraries in an RNAi reporter assay. The procedure revealed a very significant and stem sequencedependent effect of the loop on shRNA function and although neither strong consensus loop sequence nor structural motifs could be identified, a preferred loop sequence (59-UGUGCUU-39) was found to support robust knock down with little stem sequence dependency. These findings will serve as a guide for designing shRNAs with improved knock down capacity. [ABSTRACT FROM AUTHOR]

NRAS is a proto-oncogene involved in numerous myeloid malignancies. Here, we report on a mouse line bearing a single retroviral long terminal repeat inserted into Nras. This genetic modification resulted in an increased level of wild type Nras mRNA giving the possibility of studying the function and activation of wild type NRAS. Flow cytometry was used to show a variable but significant increase of immature myeloid cells in spleen and thymus, and of T- cells in the spleen. At an age of one week, homozygous mice began to retard compared to their wild type and heterozygous littermates. Two weeks after birth, animals started to progressively lose weight and die before weaning. Heterozygous mice showed a moderate increase of T-cells and granulocytes but survived to adulthood and were fertile. In homozygous and heterozygous mice Gfi1 and Gcsf mRNA levels were upregulated, possibly explaining the increment in immature myeloid cells detected in these mice. The short latency period indicates that Nras overexpression alone is sufficient to cause dose-dependent granulocytosis and Tcell expansion. [ABSTRACT FROM AUTHOR]

Aims We have previously characterized a cGMP-dependent Ca2+-activated Cl– current in vascular smooth muscle cells (SMCs) and have shown its dependence on bestrophin-3 expression. We hypothesize that this current is important for synchronization of SMCs in the vascular wall. In the present study, we aimed to test this hypothesis by transfecting rat mesenteric small arteries in vivo with siRNA specifically targeting bestrophin-3. Methods and results The arteries were tested 3 days after transfection in vitro for isometric force development and for intracellular Ca2+ in SMCs. Bestrophin-3 expression was significantly reduced compared with arteries transfected with mutated siRNA. mRNA levels for bestrophin-1 and -2 were also significantly reduced by bestrophin-3 down-regulation. This is suggested to be secondary to specific bestrophin-3 down-regulation since siRNAs targeting different exons of the bestrophin-3 gene had identical effects on bestrophin-1 and -2 expression. The transfection affected neither the maximal contractile response nor the sensitivity to norepinephrine and arginine-vasopressin. The amplitude of agonist-induced vasomotion was significantly reduced in arteries down-regulated for bestrophins compared with controls, and asynchronous Ca2+ waves appeared in the SMCs. The average frequency of vasomotion was not different. 8Br-cGMP restored vasomotion in arteries where the endothelium was removed, but oscillation amplitude was still significantly less in bestrophin-down-regulated arteries. Thus, vasomotion properties were consistent with those previously characterized for rat mesenteric small arteries. Data from our mathematical model are consistent with the experimental results. Conclusion This study demonstrates the importance of bestrophins for synchronization of SMCs and strongly supports our hypothesis for generation of vasomotion. [ABSTRACT FROM AUTHOR]

Background: Insertional mutagenesis screens in the mouse are an acknowledged approach to identify genes involved in the pathogenesis of cancer. The potential of these screens to identify genes causally involved in tumorigenesis is not only limited to the murine host, but many of these genes have also been proven to be involved in the oncogenic process in man. Results: Through an insertional mutagenesis screen applying murine leukemia viruses in mouse, we found that Cd74 was targeted by proviral insertion in tumors of B-cell origin. This locus encodes a protein playing crucial roles in antigen presentation and B-cell homeostasis, and its deregulation is often associated with cancer in man. The distribution of insertions within the Cd74 locus prompted the identification of an alternative transcript initiated in intron 1 of Cd74 encoding an N-terminally truncated Cd74 isoform in tissues from un-infected mice, and transcriptional activation assays revealed a positive effect on the novel intronic promoter by a formerly described intronic enhancer in the Cd74 locus. Furthermore, we show that the new Cd74 isoform is IFNγ inducible and that its expression is differentially regulated from the canonical Cd74 isoform at the transcriptional level. Conclusions: We here identify Cd74 as a common insertion site in murine B-lymphomas and describe a novel IFNγ-inducible murine Cd74 isoform differentially regulated from the canonical isoform and expressed under the control of an intronic promoter. The distribution and orientation of proviral insertion sites within the Cd74 locus underscores the causal involvement of the isoforms in the murine B-lymphomagenic process. [ABSTRACT FROM AUTHOR]

Background: SL3-2 is a unique polytropic murine gammaretroviral isolate that is only able to infect murine cells. We have previously shown that two mutations R212G and T213I located on the surface of the receptor binding domain in a region designated the VR3 loop can alter the species tropism of this envelope protein. This location suggests that the VR3 loop composition has an influence on receptor interaction and thereby affects binding as well as superinfection resistance. In order to investigate this further, we have studied the binding and interference patterns of the SL3-2 envelope and its mutants. Results: We find unexpectedly that wild type SL3-2 envelope binds equally well to both permissive and nonpermissive cells, indicating a post binding defect when interacting with the human Xpr1. Using replication competent viruses containing envelopes from SL3-2 or its mutants we find that the same amino acid mutations can dramatically alter the interference profile of this polytropic ENV, suggesting that the same amino acid changes that cause the post binding defect also influence interaction with the receptor. Conclusions: The envelope protein of SL3-2 MLV shows an entry defect on non-murine cells. This is coupled to a dramatically reduced ability to interfere with entry of other polytropic viruses. Two point mutations in the VR3 loop of the receptor binding domain of this envelope result both in a much increased interference ability and in removing the post-binding defect on non-murine cells, suggesting that both of these phenotypes are a consequence of insufficient interaction between the envelope and the receptor. [ABSTRACT FROM AUTHOR]

Background: Most human endogenous retroviruses (HERVs) invaded our genome at least 25 million years ago. The majority of the viral genes are degenerated, since no selection preserves them within the genome. However, a few intact and very old HERV genes exist, and likely are beneficial for the host. We here address evolutionary aspects of two HERV-V envelope genes, ENVV1 and ENVV2, located in tandem and containing a long open reading frame. Results: The ENVV2 gene is preserved with an intact reading frame during simian evolution, but none of the ENVV genes are found in the prosimian species tested. While we observe many transposon insertions in the gag and pol regions of the ERV-V2 provirus, the ENVV2 genes have escaped transposon crossfire in all species tested. Additional analysis of nucleotide substitutions provides further strong evidence of purifying selection on the ENVV2 gene during primate evolution. The other copy, ENVV1, seems to be involved in gene conversion of the major part of the envelope. Furthermore, ENVV1 and ENVV2 show placenta-specific expression in human and a baboon species. Conclusion: Our analyses show that ERV-V entered our genome after the split between simian and prosimian primates. Subsequent purifying selection and gene conversion have preserved two copies of the ENVV envelope gene in most species. This is the first case of gene conversion involving long open reading frames in HERVs. Together with the placenta-specific expression of the human and baboon ENVV1 and ENVV2 envelope genes, these data provide strong evidence of a beneficial role for the host. [ABSTRACT FROM AUTHOR]

Background: Mutations of an alternative splice donor site located within the gag region has previously been shown to broaden the pathogenic potential of the T-lymphomagenic gammaretrovirus Moloney murine leukemia virus, while the equivalent mutations in the erythroleukemia inducing Friend murine leukemia virus seem to have no influence on the disease-inducing potential of this virus. In the present study we investigate the splice pattern as well as the possible effects of mutating the alternative splice sites on the oncogenic properties of the B-lymphomagenic Akv murine leukemia virus. Results: By exon-trapping procedures we have identified a novel gammaretroviral exon, resulting from usage of alternative splice acceptor (SA') and splice donor (SD') sites located in the capsid region of gag of the B-cell lymphomagenic Akv murine leukemia virus. To analyze possible effects in vivo of this novel exon, three different alternative splice site mutant viruses, mutated in either the SA', in the SD', or in both sites, respectively, were constructed and injected into newborn inbred NMRI mice. Most of the infected mice (about 90%) developed hematopoietic neoplasms within 250 days, and histological examination of the tumors showed that the introduced synonymous gag mutations have a significant influence on the phenotype of the induced tumors, changing the distribution of the different types as well as generating tumors of additional specificities such as de novo diffuse large B cell lymphoma (DLBCL) and histiocytic sarcoma. Interestingly, a broader spectrum of diagnoses was made from the two single splice-site mutants than from as well the wild-type as the double splice-site mutant. Both single- and double-spliced transcripts are produced in vivo using the SA' and/or the SD' sites, but the mechanisms underlying the observed effects on oncogenesis remain to be clarified. Likewise, analyses of provirus integration sites in tumor tissues, which identified 111 novel RISs (retroviral integration sites) and 35 novel CISs (common integration sites), did not clearly point to specific target genes or pathways to be associated with specific tumor diagnoses or individual viral mutants. Conclusion: We present here the first example of a doubly spliced transcript within the group of gammaretroviruses, and we show that mutation of the alternative splice sites that define this novel RNA product change the oncogenic potential of Akv murine leukemia virus. [ABSTRACT FROM AUTHOR]

The human immunodeficiency virus type 1 (HIV-1) is the primary cause of the acquired immunodeficiency syndrome (AIDS), which is a slow, progressive and degenerative disease of the human immune system. The pathogenesis of HIV-1 is complex and characterized by the interplay of both viral and host factors. An intense global research effort into understanding the individual steps of the viral replication cycle and the dynamics during an infection has inspired researchers in the development of a wide spectrum of antiviral strategies. Practically every stage in the viral life cycle and every viral gene product is a potential target. In addition, several strategies are targeting host proteins that play an essential role in the viral life cycle. This review summarizes the main genetic approaches taken in such antiviral strategies. [ABSTRACT FROM AUTHOR]

Background Human gene therapy vectors based on primate lentiviruses harbour in contrast to oncoretroviruses the risk of vector mobilization by human immunodeficiency viruses (HIV). Infection of cells transduced with a lentiviral vector by HIV could lead to packaging of the lentiviral vector RNA into HIV particles and transfer of the vector. Methods A new approach based on primer complementation was developed to reduce the risk of vector mobilization. The primer binding site (PBS) of an SIV-based vector was mutated abolishing tRNA primer binding and thus blocking reverse transcription. This block was efficiently by-passed during vector production by providing an artificial tRNA matching the mutated PBS with titers reaching 106 infectious units/ml. Results Primer-complemented SIV vectors were mobilized from transduced cells by HIV-1 >150-fold less efficiently than vectors with wild-type PBS. Mobilization of the primer-complemented SIV vector by SIV was inhibited to a lesser extent indicating reduced efficacy of the primer complementation approach for preventing mobilization of lentiviral vectors by homologous virus. The analysis of the PBS of the vector DNA in target cells transduced with vectors containing mutated PBS in the absence of a matched tRNA suggests that formation of heterozygous particles followed by priming on the helper RNA and strand switch during reverse transcription can lead to mobilization of the primer-complemented vector by SIV, but not HIV-1. Although self-inactivating vectors were more efficient in preventing vector mobilization by HIV-1 than primer-complemented vectors, mobilization remained undectable only if both approaches were combined. Conclusions The primer complementation approach should further reduce the risk of mobilization of self-inactivating SIV-based vectors by HIV-1 and thus increase their safety. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Background: To generate a replication-competent retrovirus that could be conditionally inactivated, we flanked the viral genes of the Akv murine leukemia virus with LoxP sites. This provirus can delete its envelope gene by LoxP/Cre mediated recombination and thereby allow superinfection of Cre recombinase expressing cells. Results: In our studies, the virus repeatedly infected the cell and delivered multiple copies of the viral genome to the host genome; the superinfected cells expressed a viral transgene on average twenty times more than non-superinfected cells. The insertion of multiple LoxP sites into the cellular genome also led to genomic deletions, as demonstrated by comparative genome hybridization. Conclusion: We envision that this technology may be particularly valuable for delivering transgenes and/or causing deletions. [ABSTRACT FROM AUTHOR]

Background: Human endogenous retroviruses (HERVs) comprise a large class of repetitive retroelements. Most HERVs are ancient and invaded our genome at least 25 million years ago, except for the evolutionary young HERV-K group. The far majority of the encoded genes are degenerate due to mutational decay and only a few non-HERV-K loci are known to retain intact reading frames. Additional intact HERV genes may exist, since retroviral reading frames have not been systematically annotated on a genome-wide scale. Results: By clustering of hits from multiple BLAST searches using known retroviral sequences we have mapped 1.1% of the human genome as retrovirus related. The coding potential of all identified HERV regions were analyzed by annotating viral open reading frames (vORFs) and we report 7836 loci as verified by protein homology criteria. Among 59 intact or almost-intact viral polyproteins scattered around the human genome we have found 29 envelope genes including two novel gammaretroviral types. One encodes a protein similar to a recently discovered zebrafish retrovirus (ZFERV) while another shows partial, C-terminal, homology to Syncytin (HERV-W/FRD). Conclusions: This compilation of HERV sequences and their coding potential provide a useful tool for pursuing functional analysis such as RNA expression profiling and effects of viral proteins, which may, in turn, reveal a role for HERVs in human health and disease. All data are publicly available through a database at http://www.retrosearch.dk. [ABSTRACT FROM AUTHOR]

Retroviral particles contain a diploid RNA genome which serves as template for the synthesis of double-stranded DNA in a complex process guided by virus-encoded reverse transcriptase. The dimeric nature of the genome allows the proceeding polymerase to switch templates during copying of the copackaged RNA molecules, leading to the generation of recombinant proviruses that harbor genetic information derived from both parental RNAs. Template switching abilities of reverse transcriptase facilitate the development of mosaic retroviruses with altered functional properties and thereby contribute to the restoration and evolution of retroviruses facing altering selective forces of their environment. This review focuses on the genetic patchwork of retroviruses and how mixing of sequence patches by recombination may lead to repair in terms of re-established replication and facilitate increased viral fitness, enhanced pathogenic potential, and altered virus tropisms. Endogenous retroelements represent an affluent source of functional viral sequences which may hitchhike with virions and serve as sequence donors in patch repair. We describe here the involvement of endogenous viruses in genetic reassortment and patch repair and review important examples derived from cell culture and animal studies. Moreover, we discuss how the patch repair phenomenon may challenge both safe usage of retrovirus-based gene vehicles in human gene therapy and the use of animal organs as xenografts in humans. Finally, the ongoing mixing of distinct human immunodeficiency virus strains and its implications for antiviral treatment is discussed.Copyright © 2000 National Science Council, ROC and S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

The relA gene product, ATP:GTP 3′-pyrophosphotransferase (stringent factor) has been isolated homogeneous form from an Escherichia coli strain polyploid for this gene at a yield of 1 mg/100 g cells and at a specific activity in a ribosome-activated assay at 37 °C of 120 μmol guanosine pentaphosphate formed min-1 mg protein-1. The specific activity in a methanol-activated assay at 25 °C was found to be 4 μmol guanosine pentaphosphate formed min-1 mg protein -1. These values are about 100 times higher than reported by others. Our further studies of this enzyme led to the following results. Antibodies raised against this enzyme inhibit the ribosome-activated synthesis of guanosine tetraphosphate and pentaphosphate but have no effect on the much slower synthesis, detected in the absence of ribosomes. The amount of stringent factor in the rel A+ strain CP78 is estimated to about 1 copy per 200 ribosomes. The amount of antibody-binding material in CP79 (relA) is at least 5 times lower. [ABSTRACT FROM AUTHOR]

We have recently characterized in smooth muscle cells a unique cGMP-dependent Ca2+-activated Cl- current (ICl(cGMP-Ca)) that co-exists with a "classical" Ca2+-activated Cl- current. We hypothesized that bestrophin-4 (a product of the VMD2-like 3 gene) could be responsible for the ICl(cGMP-Ca) based on similarities between membrane current produced by bestrophin heterologous expression and this endogenous current. This was supported by a similar distribution pattern of the ICl(cGMP-Ca) and the bestrophin expression. To test this hypothesis siRNA-mediated downregulation of gene expression was used. Cultured aortic smooth muscle cells (A7r5) were transfected with siRNA directed against bestrophin-4 and cultured for 3 days. The efficiency of transfection was demonstrated by specific perinuclear fluorescence of Cy3-labelled siRNA. The downregulation of targeted protein expression was controlled by qPCR and Western blot. The downregulation of bestrophin-4 expression (by 88% in mRNA) with siRNA was a associated with significant reduction (by 83%) of the ICl(cGMP-Ca) while the "classical" Ca2+-activated Cl- current was not affected. Our studies provide evidence that bestrophin-4 is responsible for the ICl(cGMP-Ca) in smooth muscle cells. This study presents a novel efficient technique for specific downregulation of gene expression in blood vessels, much needed in studies of vascular function. [ABSTRACT FROM AUTHOR]