Evidence for translation of VP3 of avian polyomavirus BFDV by leaky ribosomal scanning

Summary.  Due to several incomplete splicing reactions, budgerigar fledgling disease virus (BFDV) late mature mRNAs are either bicistronic or polycistronic with an agnogene located upstream of viral protein (VP) genes. While the bicistronic mRNAs code for the vast majority of VP1, the polycistronic mRNAs contain the coding sequences of VP2, VP3, and VP1 (as the most distal cistron relative to VP2 and VP3). In this work, the translation initiation mechanism of VP3 was investigated in chicken embryo fibroblast cells by transfection of a series of BFDV mutant clones and transient reporter gene chloramphenicol acetyltransferase (CAT) expression assay, leading to the conclusion that BFDV VP3 was translated by leaky ribosomal scanning. Furthermore, thanks to the high sensitivity of CAT assay experiment, we were able to demonstrate that ribosomes could reach VP1-AUG and initiate translation after scanning through 900 nucleotides on the unspliced polycistronic mRNA. Accepted August 28, 1999/Received June 4, 1999     

Interferon inhibits dengue virus infection by preventing translation of viral RNA through a PKR-independent mechanism.

Previously, we demonstrated that pretreatment of cells with interferon (IFN) alpha + gamma or beta + gamma inhibited dengue virus (DV) replication. In this study, experiments were performed to better define the mechanism by which IFN blocks the accumulation of dengue virus (DV) RNA. Pretreatment of human hepatoma cells with IFN beta + gamma did not significantly alter virus attachment, viral entry, or nucleocapsid penetration into the cytoplasm. The inhibitory effect of IFN was retained even when naked DV RNA was transfected directly into cells, confirming that steps associated with viral entry were not the primary target of IFN action. Biosynthetic labeling experiments revealed that IFN abolished the translation of infectious viral RNA that occurred prior to RNA replication. Subcellular fractionation experiments demonstrated that IFN did not significantly alter the ability of viral RNA to attach to ribosomes. The antiviral effect of IFN appeared independent of the IFN-induced, double-stranded RNA-activated protein kinase (PKR) and RNase L, as genetically deficient PKR- RNase L- cells that were infected by DV retained sensitivity to inhibition by IFN. We conclude that IFN prevents DV infection by inhibiting translation of the infectious viral RNA through a novel, PKR-independent mechanism.     

Internal initiation of translation of bovine viral diarrhea virus RNA.

Initiation of translation on the bovine viral diarrhea virus (BVDV) internal ribosomal entry site (IRES) was reconstituted in vitro from purified translation components to the stage of 48S ribosomal initiation complex formation. Ribosomal binding and positioning on this mRNA to form a 48S complex did not require the initiation factors eIF4A, eIF4B, or eIF4F, and translation of this mRNA was resistant to inhibition by a trans-dominant eIF4A mutant that inhibited cap-mediated initiation of translation. The BVDV IRES contains elements that are bound independently by ribosomal 40S subunits and by eukaryotic initiation factor (eIF) 3, as well as determinants that mediate direct attachment of 43S ribosomal complexes to the initiation codon.     

A shine-dalgarno-like sequence mediates in vitro ribosomal internal entry and subsequent scanning for translation initiation of coxsackievirus B3 RNA

Translation initiation of coxsackievirus B3 (CVB3) RNA is directed by an internal ribosome entry site (IRES) within the 5' untranslated region. However, the details of ribosome-template recognition and subsequent translation initiation are still poorly understood. In this study, we have provided evidence to support the hypothesis that 40S ribosomal subunits bind to CVB3 RNA via basepairing with 18S rRNA in a manner analogous to that of the Shine-Dalgarno (S-D) sequence in prokaryotic systems. We also identified a new site within both the 18S rRNA and the polpyrimidine-tract sequence of the IRES that allows them to form stronger sequence complementation. All these data were obtained from in vitro translation experiments using mutant RNAs containing either an antisense IRES core sequence at the original position or site-directed mutations or deletions in the polypyrimidine tract of the IRES. The mutations significantly reduced translation efficiency but did not abolish protein synthesis, suggesting that the S-D-like sequence is essential, but not sufficient for ribosome binding. To determine how ribosomes reach the initiation codon after internal entry, we created additional mutants: when the authentic initiation codon at nucleotide (nt) 742 was mutated, a 180-nt downstream in-frame AUG codon at nt 922 is able to produce a truncated smaller protein. When this mutation was introduced into the full-length cDNA of CVB3, the derived viruses were still infectious. However, their infectivity was much weaker than that of the wild-type CVB3. In addition, when a stable stem-loop was inserted upstream of the initiation codon in the bicistronic RNA, translation was strongly inhibited. These data suggest that ribosomes reach the initiation codon from the IRES likely by scanning along the viral RNA.     

核酶在细胞外切割HCV核心区RNA的研究

目的 研究核酶在细胞外切割HCV的作用。方法 设计核酶cDNA序列,构建核酶重组质粒及HCV核心区基因cDNA重组质粒。分别进行体外转录,并加入γ-^32P ATP以标记HCV RNA。将核酶RNA、HCV核心区RNA、RNA酶抑制剂及反应缓冲液混事浊国育,以核酶RNA切割HCV RNA。通过变性聚 烯酰胺凝胶电泳及放射自显影来分析结果。结果 β－半乳糖苷酶表型筛选均可见蓝色及白色菌落生长;核酶重组质粒直接测序结果见预期要苷酸序列;HCV重组质粒限制笥酶切分析见410bp条带。核酶切割反应显示：反应时间为15和30min时可见453、307、146nt3条带。反应时间为60min时仅见307及146nt2条带。结论 核酶重组质粒构建成功,所设计核酶对HCV有切割作用。     

Efficient extraction of viral DNA and viral RNA by the Chemagic viral DNA/RNA kit allows sensitive detection of cytomegalovirus, hepatitis B virus, and hepatitis G virus by PCR

The Chemagic Viral DNA/RNA kit was evaluated for extraction of cytomegalovirus (CMV), hepatitis B virus (HBV), and hepatitis G virus (HGV) by using the QIAamp DNA Blood Mini kit and the QIAamp Viral RNA Mini kit as reference protocols. The extraction efficiencies of the different kits for CMV DNA and HBV DNA were not distinguishable, but the extraction efficiency for HGV RNA was better with the Chemagen protocol. All clinical specimens tested HBV DNA- or HGV RNA-positive after QIAGEN protocols for extraction were confirmed by using the Chemagen protocol. The Chemagen kit failed to confirm one of 75 CMV DNA-positive specimens. Thus, a new competitive extraction method using a technology with a high potential for automation is available.     

乙型肝炎病毒感染时的C基因热点变异

为了解乙型肝炎病毒感染在不同病变时的Ｃ基因热点变异，对９１名感染者以限制片段长度多态性技术检测前Ｃ终２８和Ｃ区Ｌ９７点突变。在急性乙型肝炎和慢性无症状携带者几无突变、在慢性持续性肝炎中罕见，而在慢性活动性肝炎和活动性肝硬变中分别达８０％和７８％，肝细胞癌中为６１％。ＨＢｅＡｇ（＋）的慢性活动性肝炎和活动性肝硬变１６例中，混合有终２８变异１１例，抗－ＨＢｅ（＋）病例中亦有野毒株混合。Ｃ区密码９７亮氨酸变异（Ｌ９７）亦见混合。野毒株和变异株在病程中有消长，Ｃ基因的热点变异与病变活动性密切相关。第一军医大学南方医院     

Evidence for control of translation of the viral genome during replication of Mengo virus and poliovirus.

An investigation of the synthesis of virus-specific polypeptides in Mengo virus-infected L cells and poliovirus-infected HeLa cells has shown that, from early to late log phase of virus production, there is a progressive increase in the ratio of capsid to noncapsid polypeptides synthesized. Comparable studies carried out in the presence of amino acid analogs have revealed that during the same time period there is a progressive decrease in the ratio of polyprotein (the presumed translation product of the entire genome) to capsid precursor protein synthesized. Both sets of data are compatible with the hypothesis that, during replication of these viruses, translation of the viral genome is subject to some kind of control.     

Evaluation of a new molecular assay for detection of human immunodeficiency virus type 1 RNA, hepatitis C virus RNA, and hepatitis B virus DNA.

BACKGROUND: Rapid, sensitive, specific, and cost-effective screening of donated blood to prevent transmission of infectious agents remains challenging. In recent years, incorporation of nucleic acid testing for HIV-1 and HCV RNA improved blood safety by reducing the window period between infection and serologic detection. For HBV infection, this window period with most serologic assays is 50-60 days. Adding a nucleic acid test (NAT) for HBV DNA with existing NATs for HIV-1 and HCV RNA would further improve blood safety and blood screening efficiency. OBJECTIVE: To evaluate the Procleix Ultrio Assay for simultaneous detection of HIV-1 and HCV RNA and HBV DNA and corresponding discriminatory assays. STUDY DESIGN: The performance of these assays, which utilize the same technology and assay format as the Procleix HIV-1/HCV assay, was determined using relevant clinical specimens and analytical sensitivity and specificity panels. RESULTS: The Procleix Ultrio Assay demonstrated specificity of > or =99.5% in healthy donor blood specimens and in plasma containing potentially interfering substances or other blood-borne pathogens. Assay sensitivity demonstrated >95% detection of 100copies/mL, 30IU/mL, and 15IU/mL for HIV-1 and HCV RNA, and HBV DNA, respectively. The assay detects all known HIV-1 subtypes and HCV and HBV genotypes and is highly reproducible. Statistical analysis using receiver operating characteristic plots demonstrated wide analyte cutoff values for each assay associated with assay specificity and sensitivity of > or =99.5%. CONCLUSIONS: In this investigational study, the Procleix Ultrio Assay sensitivity and specificity were similar to existing NATs used in blood-bank settings to detect HIV-1 and HCV RNA and provided equivalent sensitivity and specificity for detection of HBV DNA. Using this combination assay, blood safety may be improved and the multiplex format enhances blood screening efficiency. The throughput capability of this assay is compatible with large volume processing and the chemistry is adaptable to full automation.     

Utilization of RNA polymerase I promoter and terminator sequences to develop a DNA transfection system for the study of hepatitis C virus internal ribosomal entry site-dependent translation.

BACKGROUND: Hepatitis C virus (HCV) causes severe liver diseases in a large population worldwide. HCV protein translation is controlled by an internal ribosomal entry site (IRES) within the 5'-untranslated region (UTR). HCV IRES-dependent translation is critical for HCV-associated pathogenesis. OBJECTIVE: To develop a plasmid DNA transfection system by using RNA polymerase I promoter and terminator sequences for studying HCV IRES-dependent translation. STUDY DESIGN: A gene cassette containing HCV 5'-UTR, Renilla luciferase reporter gene, and HCV 3'-UTR was inserted between RNA polymerase I promoter and terminator sequences. HCV IRES-directed translation was determined by luciferase assay after transfection. RESULTS: Transfection of the RNA polymerase I-HCV IRES plasmid into human hepatoma Huh-7 and HepG2 cells resulted in luciferase gene expression. Deletion of the IIIf domain in HCV IRES dramatically reduced luciferase activity. CONCLUSION: Our results indicated that the plasmid vector system-based on RNA polymerase I promoter and terminator sequences represents an effective approach for the study of HCV IRES-dependent translation.     

Delta virus superinfection in a patient with chronic viral hepatitis B

Hepatitis-Delta virus is a defective RNA virus enclosing the Delta antigen and genome within a coat of hepatitis B surface antigen (HBsAg). Prevalence of Delta virus is limited to individuals with hepatitis B infection. Two modes of infection have been identified: coinfection with hepatitis virus B of healthy individuals and superinfection of HBsAg carriers. In a prospective study of 485 liver biopsies from HBsAg seropositive patients, 320 non-replicative HBsAg carriers (without evidence of core antigen) were discovered. In only one of these cases could a Delta virus superinfection be confirmed by immunohistology. It caused a shift from a preexisting chronic persistent to a chronic active hepatitis. This is the first case of chronic Delta virus infection confirmed by immunhistology in the G.D.R.     

The role of viral load determination for the management of human immunodeficiency virus, hepatitis B virus and hepatitis C virus infection.

During the last 5 years, considerable scientific and financial efforts have been made in the development of quantitative nucleic acid detection technology. For detection of human immunodeficiency virus (HIV), quantitative culture is time consuming, cumbersome and requires appropriate laboratory safety equipment. Quantitative determination of p24 antigen by enzyme immunoassay is of limited value due to its relatively poor sensitivity. Therefore, quantitative determination of viral load using nucleic acid amplification techniques is the most accurate, prognostic marker for HIV type 1 infection, independently of the CD4+ cell count. Hepatitis B virus (HBV) is not cultivable in vitro. Serological assays allow an accurate diagnosis and follow-up of acute or chronic infection. Quantification of HBV DNA is used for the monitoring of antiviral therapy, determination of infectivity and for resolution of unclear serological profiles, e.g. isolated anti-HBc reactivity, as well as for patients in which HBV mutants are suspected. Hepatitis C virus (HCV) can only be detected by molecular based assays because no cell culture system, which permits a reliable isolation of clinical specimens, is currently available. Furthermore, early diagnosis and follow-up of infection cannot be achieved with antibody serology. The prognostic relevance of quantitative HCV RNA determination is of limited value for the long-term prognosis of chronic hepatitis C. However, viral load may predict the outcome of antiviral therapy. Genetic diversity is another challenge for HCV RNA quantification.     

Analysis of viral proteins in circulating immune complexes from chronic carriers of hepatitis B virus.

Sera from 54 children (mean age 5.8 years) with chronic hepatitis B virus (HBV) infection were investigated for the presence of immune complexes containing HBV proteins. Clinical diagnosis was established by histology and biochemical markers and included chronic persistent (36 cases) or chronic aggressive (seven) hepatitis, liver cirrhosis (six) and HBV-mediated membranous glomerulonephritis (five). Circulating immune complexes were precipitated with 2.5% polyethylene glycol and analysed by immune blot using monoclonal antibodies against S, pre-S2 glycopeptide, pre-S1 and HBe/c epitopes. All sera, including those from 11 healthy HBV-negative blood donors contained PEG-precipitable substances, but the amount of precipitate did not correlate with the presence or amount of HBV proteins. The great majority (36 out of 40) of HBeAg-positive patients contained HBs proteins in immune complexes, but no detectable HBe protein. The immune complexes usually contained more pre-S1 than the free HBsAg particles from the same patient. The precipitates of anti-HBe-positive patients rarely contained HBV proteins (two out of 14) and, if so, in low amounts. During follow up of six patients we found that high levels of HBs-containing immune complexes may be correlated with subsequent elimination of HBV. This elimination is possibly initiated by binding of anti-pre-S1 antibodies to HBV and HBs particles.