线粒体DNA复制及其调控

从线粒体DNA复制的模型与机制、复制的调控、复制忠实性及其损伤修复3个方面对近年来的研究文献进行了总结.在复制的模型与机制方面,对传统的D环复制的细节有了更深入的了解,新的实验方法的结果显示,在哺乳动物中还存在着链结合单向复制和链结合双向复制2种模型.在线粒体DNA复制的调控方面,近年来研究较多的调控因子主要包括mtDNA聚合酶γ、线粒体单链结合蛋白(mtSSB)、引物酶、解旋酶、连接酶、拓扑异构酶、转录因子mtTFA等,介绍了这些因子的最新研究进展及调控机制;对mtDNA复制时期和拷贝数量调控机制的研究也有突破,确定了Abf2p是mtDNA复制时期与拷贝数目的调控因子.在mtDNA复制的忠实性及其损伤修复研究方面,主要涉及到DNA Polγ的校正功能、错配修复、重组修复、DNA切除修复等,在mtDNA损伤修复中仅存在碱基切除修复机制,缺少核苷酸切除修复机制.     

Stress responses and replication of plasmids in bacterial cells

Plasmids, DNA (or rarely RNA) molecules which replicate in cells autonomously (independently of chromosomes) as non-essential genetic elements, play important roles for microbes grown under specific environmental conditions as well as in scientific laboratories and in biotechnology. For example, bacterial plasmids are excellent models in studies on regulation of DNA replication, and their derivatives are the most commonly used vectors in genetic engineering. Detailed mechanisms of replication initiation, which is the crucial process for efficient maintenance of plasmids in cells, have been elucidated for several plasmids. However, to understand plasmid biology, it is necessary to understand regulation of plasmid DNA replication in response to different environmental conditions in which host cells exist. Knowledge of such regulatory processes is also very important for those who use plasmids as expression vectors to produce large amounts of recombinant proteins. Variable conditions in large-scale fermentations must influence replication of plasmid DNA in cells, thus affecting the efficiency of recombinant gene expression significantly. Contrary to extensively investigated biochemistry of plasmid replication, molecular mechanisms of regulation of plasmid DNA replication in response to various environmental stress conditions are relatively poorly understood. There are, however, recently published studies that add significant data to our knowledge on relations between cellular stress responses and control of plasmid DNA replication. In this review we focus on plasmids derived from bacteriophage lambda that are among the best investigated replicons. Nevertheless, recent results of studies on other plasmids are also discussed shortly.     

细菌RNA结合蛋白Hfq的DNA压缩和复制作用研究进展

RNA结合蛋白(RNA-Binding Protein)Hfq是一种重要的细菌转录后调节因子,之前对Hfq的研究大多集中在该蛋白对小分子非编码RNA (Small Non-Coding RNA,sRNA)和mRNA的作用上。Hfq最典型的功能是促进sRNA与其靶标mRNA碱基配对,在转录后介导对RNA的稳定性和翻译的调控。此外,Hfq也能与多种蛋白质直接或间接相互作用。然而,近年来的研究表明,除了RNA和蛋白质,Hfq还可以与DNA相互作用,在DNA压缩(DNA Compaction)和DNA复制(DNA Replication)等多种DNA代谢过程中发挥直接或间接的调控作用。额外的靶标和功能的鉴定将进一步夯实Hfq作为细菌中多种代谢途径核心调控因子的重要地位,也表明该蛋白的功能并不局限于其在RNA和蛋白质代谢中的作用。本文总结了Hfq在DNA代谢调控中的近几年最新研究进展,并展望了其前景。     

Inheritance of the replication complex: a unique or common phenomenon in the control of DNA replication?

Early models of the regulation of initiation of DNA replication by protein complexes predicted that binding of a replication initiator protein to a replicator region is required for initiation of each DNA replication round, since after the initiation event the replication initiator should dissociate from DNA. It was, therefore, assumed that binding of the replication initiator is a signal for triggering DNA replication. However, more recent investigations have revealed that in many replicons this is not the case. Studies on the regulation of the replication of plasmids derived from bacteriophage lambda demonstrated that, once assembled, the replication complex can be inherited by one of the two daughter plasmid copies after each replication round and may function in subsequent replication rounds. Since this DNA-bound protein complex bears information about specific initiation of DNA replication, this phenomenon has been called "protein inheritance." A similar phenomenon has recently been reported for oriJ-based plasmids. Moreover, the current model of the initiation of DNA replication in the yeast Saccharomyces cerevisiae proposes that the origin recognition complex (ORC) remains bound to one copy of the ori sequence (the ARS region) after initiation of DNA replication. Thus, it seems plausible that protein inheritance is not unique for lambda plasmids, but may be a common phenomenon in the control of DNA replication, at least in microbes.     

GSK-3-associated signaling is crucial to virus infection of cells

Signal transduction pathways play important roles in virus infection, replication, and associated pathogenesis. Some of the best understood cell signaling networks are crucial to virus infections such the mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K), protein kinase C (PKC), and the WNT/β-catenin pathways. Glycogen synthase kinase-3 (GSK-3) is a lesser known signaling molecule in the field of virus research. Interestingly, GSK-3 forms the crux of multiple cell signaling pathways. However, recent studies indicate that GSK-3 may perform key roles in the response to viral infection, replication and pathogenesis. The effects of activated or inactivated forms of GSK-3 on virus infection are still not yet clearly understood phenomenon. The comprehension of the molecular mechanisms underlying the regulation of GSK-3-associated signaling pathways in terms of different stages of virus replication could be important not only to understand the pathogenesis of virus, but also possibly leading to new therapeutic targets. This review will focus on recent advances in understanding the roles of GSK-3 on viral replication, pathogenesis and the immune responses.     

DNA helicase requirements for DNA replication during bacteriophage T4 infection.

The lytic bacteriophage T4 uses multiple mechanisms to initiate the replication of its DNA. Initiation occurs predominantly at replication origins at early times of infection, but there is a switch to genetic recombination-dependent initiation at late times of infection. The T4 insertion-substitution system was used to create a deletion in the T4 dda gene, which encodes a 5'-3' DNA helicase that stimulates both DNA replication and recombination reactions in vitro. The deletion caused a delay in T4 DNA synthesis at early times of infection, suggesting that the Dda protein is involved in the initiation of origin-dependent DNA synthesis. However, DNA synthesis eventually reached nearly wild-type levels, and the final number of phages produced per bacterium was similar to that of the wild type. When the dda mutant phage also contained a mutation in T4 gene 59 (a gene normally required only for recombination-dependent DNA replication), essentially no DNA was synthesized. Recent in vitro studies have shown that the gene 59 protein loads a component of the primosome, the T4 gene 41 DNA helicase, onto DNA. A molecular model for replication initiation is presented that is based on our genetic data.     

肽核酸在基因诊断和治疗中的研究进展

肽核酸是一种以多肽为骨架,类似核苷酸的物质。它不带电荷,能抵抗核酸酶和蛋白酶的降解;它与DNA或RNA杂交特异性很强,可与靶基因形成稳定的三螺旋结构。肽核酸能够抑制基因的复制、转录、逆转录和翻译过程,在基因诊断及治疗方面有着广泛的用途。