Sequence-dependent Termination of Mammalian DNA Polymerase Reaction by a New Platinum Compound, (–)-(R)-2-Aminomethylpyrrolidine(1,1-cyclobutane-dicarboxylato)-2-platinum(II) Monohydrate

We examined the mechanisms of the inhibition of DNA synthesis by a new platinum compound, (-)-( R )-2-aminomethylpyrrolidine(1,1-cyclobutane-dicarboxylato)-2-platinum(II) monohydrate (DWA-2114R), a derivative of the antitumor drug cis- diamminedichloroplatinum(II) (CDDP), using prokaryotic and eukaryotic DNA polymerases. Preincubating activated DNA with CDDP or DWA-2114R reduced its template activity for prokaryotic and eukaryotic DNA polymerases in a dose-dependent manner. DWA2114R required six times greater drug concentration and two times longer incubation time to show the same decrease of the template activity compared to CDDP. Treatment of primed pUC118 ssDNA templates with the two drugs followed by second-strand synthesis by prokaryotic and eukaryotic DNA polymerases revealed that DWA2114R bound to DNA in a similar manner to CDDP and these adducts blocked DNA elongation by DNA polymerases of eukaryotes as well as of prokaryotes. With these two drugs, the elongations by E. coli DNA polymerase I (Klenow fragment), T7 DNA polymerase and calf thymus DNA polymerase α were strongly arrested at guanine-guanine sequences (GG). Stop bands were also observed at adenine-guanine sequences (AG) guanine-adenine-guanine sequences (GAG) and mono-guanine sequence (G). Calf testis DNA polymerase β was also arrested efficiently at AG, GAG and G, but much more weakly at GG. This pattern was common to DWA2114R and CDDP.     

慢性乙肝患者血清细胞因子、乙肝病毒与肝纤维化的关系

目的：探讨慢性乙肝患血清细胞因子（TGF－β，TNF-α，IL-6，IL-8），乙肝病毒（HBV）对肝纤维化（HA，PCⅢ，C-Ⅳ，LN）的影响作用。方法：采用ELISA和RIA方法检测171例慢性乙肝患血清TGF－β，TNF-α，IL-6，IL-8，HLA，PCǚ，C-Ⅳ，LN的水平，HBV－DNA定量检测采用PCR方法。结果：慢性乙肝患血清TGF－β，TNF-α，IL-6，IL-8，HA，PCⅢ，C-Ⅳ，LN的含量均不同程度高于对照组，且随肝损害程度的加重而升高，与肝损害程度呈正相关关系（P＜0．05或P＜0．01）；须血清TGF－β1水平与血清HA，PCⅢ，C-Ⅳ，LN水平具有直线相关关系。HBV－DNA阳性组（Ⅱ组）均高于HBV－DNA阴性组（I组），且在慢性中，重度肝炎间差异显（P＜0．05）。结论：血清TGF－β，TNF-α，IL-6，IL-8参与慢性乙肝的发病机制及肝纤维化的形成，且与病毒复制的活跃程度相关。     

Production and release of infectious hepatitis C virus from human liver cell cultures in the three-dimensional radial-flow bioreactor

Lack of efficient culture systems for hepatitis C virus (HCV) has been a major obstacle in HCV research. Human liver cells grown in a three-dimensional radial-flow bioreactor were successfully infected following inoculation with plasma from an HCV carrier. Subsequent detection of increased HCV RNA suggested viral replication. Furthermore, transfection of HCV RNA transcribed from full-length cDNA also resulted in the production and release of HCV virions into supernatant. Infectivity was shown by successful secondary passage to a new culture. Introduction of mutations in RNA helicase and polymerase regions of HCV cDNA abolished virus replication, indicating that reverse genetics of this system is possible. The ability to replicate and detect the extracellular release of HCV might provide clues with regard to the persistent nature of HCV infection. It will also accelerate research into the pathogenicity of HCV, as well as the development of prophylactic agents and new therapy.     

The linear plasmid pSA3239 is essential for the replication of the Streptomyces lavendulae subsp. lavendulae CCM 3239 chromosome

We previously reported the complete genome of Streptomyces lavendulae subsp. lavendulae CCM 3239, containing the linear chromosome and the large linear plasmid pSA3239. Although the chromosome exhibited replication features characteristic for the archetypal end-patching replication, it lacked the tap/tpg gene pair for two proteins essential for this process. However, this archetypal tpgSa-tapSa operon is present in pSA3239. Complete genomic sequence of the S. lavendulae Del-LP strain lacking this plasmid revealed the circularization of its chromosome with a large deletion of both arms. These results suggest an essential role of pSA3239-encoded TapSa/TpgSa in the end-patching replication of the chromosome.     

Influenza A virus-induced apoptosis is a multifactorial process: exploiting reverse genetics to elucidate the role of influenza A virus proteins in virus-induced apoptosis

Three influenza viruses, A/Puerto Rico/8/34-A/England/939/69 clone 7a (H3N2), A/Fiji/15899/83 (H1N1), and A/Victoria/3/75 (H3N2), induce different levels of apoptosis in vitro at equal moi; Clone 7a > A/Victoria > A/Fiji. Previous studies have shown that several viral proteins from clone 7a and A/Fiji, including PB2, NA, NS1, M1, and M2, induce apoptosis when expressed individually fused to the herpes simplex virus tegument protein, VP22. However, this did not reflect viral protein-protein-RNA interactions known to occur within infected cells. To explore the role of viral proteins in apoptosis under infection conditions, recombinant viruses with single or triple gene exchanges were generated using A/Victoria or clone 7a as the background virus. Inserting the A/Fiji NS or PB2 gene into A/Victoria or clone 7a significantly reduced the level of apoptosis compared to the parent virus while clone 7a PA or NP genes increased apoptosis. Inserting A/Fiji NA or HA or clone 7a NS, M, NA, or HA genes individually into A/Victoria had no significant effect on apoptosis. Surprisingly, inserting the M, NA, and HA genes of A/Fiji together into clone 7a reduced apoptosis, whereas inserting clone 7a M, NA, and HA together into A/Fiji increased apoptosis. These results suggest that no single virus protein induces apoptosis and that the combination of genes required may be strain specific, highlighting the difficulty of predicting the virulence of new strains that arise in nature. No support for the view that apoptosis is essential for high virus yields was obtained as high virus yields were obtained with viruses that induced both high and low levels of apoptosis.     

丙型肝炎病毒阳性血清体外感染人肝细胞的研究

目的 研究丙型肝炎病毒(HCV)抗体(Ab)阴性,HCV-RNA阳性血清建立体外感染肝细胞模型.方法 HCV Ab阴性,HCV-RNA阳性的窗口期血清与人肝细胞共同培养,用反转录-聚合酶链反应(RT-PCR)、免疫荧光染色、Western blot、共聚焦显微镜和透射电镜等方法检测细胞内HCV核酸复制、蛋白质表达及超微结构改变.结果 细胞与病毒共同培养7～45 d,细胞内和/或培养上清中可间断检出HCV正、负链RNA;细胞浆内有HCV 核心和NS3抗原的表达;细胞超微结构有改变,并于感染后第24天时观察到类似病毒样颗粒.结论 窗口期血清中的HCV能在人肝细胞7701中复制一段时间.     

Interaction between the replicase proteins of Tomato bushy stunt virus in vitro and in vivo

Tomato bushy stunt virus (TBSV), a tombusvirus with a non-segmented, plus-stranded RNA genome, codes for p33 and p92 replicase proteins. The sequence of p33 overlaps with the N-terminal domain of p92, which also contains the signature motifs of RNA-dependent RNA polymerases (RdRps) in its non-overlapping C-terminal portion. In this research, we demonstrate in vitro interactions between p33:p33 and p33:p92 using surface plasmon resonance analysis with purified recombinant p33 and p92. The sequence in p33 involved in the above protein-protein interactions was mapped to the C-terminal region, which also contains an RNA-binding site. Using the yeast two-hybrid assay, we confirmed that two short regions within p33 could promote p33:p33 and p33:p92 interactions in vivo. Mutations in either p33 or p92 within the short regions involved in p33:p33 and p33:p92 interactions decreased the replication of a TBSV defective interfering RNA in yeast, a model host, supporting the significance of these protein interactions in tombusvirus replication.     

The Schizosaccharomyces pomberfc3 + gene encodes a homologue of the human hRFC36 and Saccharomyces cerevisiae Rfc3 subunits of replication factor C

In the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe replication factor C (RF-C) plays key roles both in chromosomal DNA replication and in DNA replication checkpoint function. At the replication fork, the five-subunit RF-C complex functions to load the trimeric polymerase accessory factor PCNA onto DNA. PCNA then acts as a sliding clamp, tethering Pol δ to the DNA to maximise its processivity. Here we describe the cloning of the S. pomberfc3 ⁺ gene, encoding a homologue of the S. cerevisiae Rfc3 and human hRFC36 proteins. The 1026 bp rfc3 ⁺ ORF is interrupted by five introns, ranging in size from 49 to 165 bp. The spliced ORF is predicted to encode a 342 amino-acid protein that is approximately 50% identical at the amino acid sequence level to the S. cerevisiae Rfc3 and human hRFC36 proteins. As expected, S. pomberfc3 ⁺ is an essential gene, with rfc3Δ cells being defective for DNA replication. Loss of rfc3 ⁺ function can be rescued by heterologous expression of either the S. cerevisiae Rfc3 or human hRFC36 proteins in S. pombe. Received: 15 October 1999     

The role of the p33:p33/p92 interaction domain in RNA replication and intracellular localization of p33 and p92 proteins of Cucumber necrosis tombusvirus

Replication of plus-stranded RNA viruses is performed by the viral replicase complex, which, together with the viral RNA, must be targeted to intracellular membranes, where replication takes place in membraneous vesicles/spherules. Tombusviruses code for two overlapping replication proteins, the p33 auxiliary protein and the p92 polymerase. Using replication-competent fluorescent protein-tagged p33 of Cucumber necrosis virus (CNV), we determined that two domains affected p33 targeting to peroxisomal membranes in yeast: an N-proximal hydrophobic trans-membrane sequence and the C-proximal p33:p33/p92 interaction domain. On the contrary, only the deletion of the p33:p33/p92 interaction domain, but not the trans-membrane sequence, altered the intracellular targeting of p92 protein in the presence of wt p33 and DI-72(+) RNA. Moreover, unlike p33, p92 lacking the trans-membrane sequence was still functional in supporting the replication of a replicon RNA in yeast, whereas the p33:p33/p92 interaction domain in both p33 and p92 was essential for replication. In addition, p33 was also shown to facilitate the recruitment of the viral RNA to peroxisomal membranes and that p33 is colocalized with (+) and (-)-stranded viral RNAs. Also, FRET and pull-down analyses confirmed that p33 interacts with other p33 molecules in yeast cells. Based on these data, we propose that p33 facilitates the formation of multimolecular complexes, including p33, p92, viral RNA, and unidentified host factors, which are then targeted to the peroxisomal membranes, the sites of CNV replication.