Molecular cloning and partial sequencing of hepatitis A viral cDNA.

Hepatitis A virus was purified from infected monkey kidney cell cultures, and the viral RNA was used to synthesize double-stranded cDNA. This cDNA was cloned either after insertion into a plasmid-primed synthesis system or after insertion into the PstI site of pBR322. The resulting clones were mapped by restriction endonuclease analysis and by cross hybridization of the viral inserts to generate a composite map which represented at least 97% of the viral genome, lacking ca. 220 bases from the 5' end of the genome. The clones were verified to be hepatitis A virus specific based on their positive hybridization to viral RNA and to total hepatitis A virus-infected cellular RNA from a heterologous marmoset host system. The nucleotide sequence of 3,054 base pairs of cDNA homologous to the 5' half of the viral genome was determined, and an open reading frame of 854 consecutive coding triplets was identified. In addition, sequences which encode the VP-1 and VP-3 viral structural proteins were located in the nucleotide sequence.     

Adaptation of hepatitis A virus strain (JaM-55) originally pathogenic for monkeys to a cell culture

The results of adaptation of hepatitis A viral strain JaM-55 to the culture of embryo kidney cells FRhk-4 from macaque Rhesus are presented. The viral strain was isolated from a M. fascicularis suffering from spontaneous hepatitis. Before inoculating the cell culture the virus was passaged twice in the M. arctoides capable of reproducing hepatitis. FRhk-4 cell line inoculation by the monkey liver extract, containing the strain HAV-YaM-55, resulted in isolation of single viral particles of hepatitis A in the preparations obtained at the first 3 passages by the 28-31 day of cultivation. Beginning from the fourth passage the abrupt increase in the number of viral particles and hepatitis A antigen was registered. There were no traces of cytopathogenic effect at any level of viral passages in the inoculated cell culture. The adapted virus contains hepatitis A viral RNA identified by spot hybridization with the cloned cDNA of hepatitis A virus.     

中国首次分离的辛德毕斯病毒XJ-160病毒株感染性全基因组cDNA克隆的构建与分析

报告了中国首次分离的辛德毕斯病毒XJ-160株的感染性全基因组cDNA克隆的构建与鉴定。利用RT—PCR方法获得覆盖病毒全长基因组的cDNA片段,以低拷贝质粒pBR322作为骨架,将基因组cDNA置于SP6RNA聚合酶启动子之后,基因组3’末端带有35个连续的A,通过DNA重组技术组装成病毒基因组全长cDNA克隆。该克隆可在大肠杆菌DH5a中稳定扩增。经体外转录,RNA转录体转染BHK-21细胞,细胞发生病变,恢复病毒滴度达到10^7～10^8PFU／ml。全基因组cDNA克隆构建过程中引入的沉默突变(8453位核苷酸由C变为T)产生XbaⅠ酶切位点作为遗传标记,在子代恢复病毒的基因组中稳定存在。从细胞病变的特征、BHK-21细胞的空斑形态、病毒的抗原性、病毒在细胞中的生长动力学特征以及对乳鼠的致病性等方面比较,恢复病毒和亲本病毒XJ-160没有显著区别,提示获得了具有感染性的XJ-160病毒全长cDNA克隆。该病毒感染性全基因组cDNA克隆可以作为反向遗传学系统,为进一步研究病毒复制和致病机制,以及开发相应的载体表达系统提供分子生物学工具。     

Direct cloning of cDNA inserts from lambda gt11 phage DNA into a plasmid vector by a novel and simple method

Bacteriophage lambda gt11 has been used quite extensively for producing cDNA libraries. The cDNA inserts are usually subcloned into a plasmid vector for large scale production and analysis. However, isolating the recombinant DNA of interest from the phage clones can be a tedious task. Since the E. coli strain Y1088 used for lambda gt11 phage infection carries a pBR322-derived plasmid endogenously, we reasoned that this endogenous plasmid could be used directly for cloning the cDNA phage insert. In this report, we describe a method in which cDNA inserts from lambda gt11 phage were cloned directly into the pBR322 plasmid vector, bypassing the time-consuming procedures of preparing plasmid DNA as a subcloning vector. This method is likely to be extended to the cloning of DNA inserts derived from other phage lambda vectors when bacteria containing endogenous pBR322 are used as host cells.     

Initiation of replication of the human hepatitis delta virus genome from cloned DNA: role of delta antigen.

Beginning with three partial cDNA clones of the RNA genome of human hepatitis delta virus (HDV), we assembled the complete 1,679-base sequence on a single molecule and then inserted a trimer of this into plasmid pSLV, a simian virus 40-based eucaryotic expression vector. This construct was used to transfect both monkey kidney (COS7) and human hepatocellular carcinoma (HuH7) cell lines. In this way we obtained replication of the HDV RNA genome and the appearance, in the nucleoli, of the delta antigen, the only known virus-coded protein. This proved both that the HDV genome could replicate in nonliver as well as liver cells and that there was no requirement for the presence of hepatitis B virus sequences or proteins. When the pSVL construct was made with a dimer of an HDV sequence with a 2-base-pair deletion in the open reading frame, genome replication was reduced at least 40-fold. However, when we cotransfected with a plasmid that expressed the correct delta antigen, the mutated dimer achieved a level of genome replication comparable to that of the nonmutated sequence. We thus conclude that the delta antigen can act in trans and is essential for replication of the HDV genome.     

Persistently infected cultures as a source of hepatitis A virus.

Primary African green monkey kidney, continuous African green monkey kidney cell line BS-C-1, and buffalo green monkey kidney cultures were infected with a uniform inoculum of hepatitis A virus (HAV). Although both the cell line BS-C-1 and primary African green monkey kidney cultures produced useful amounts of virus, HAV was detected earlier and in greater quantities in primary African green monkey kidney cultures. A persistently infected primary African green monkey kidney culture was developed. The influence of incubation time (4 to 40 days) and concentration (2 to 15%) of fetal calf serum in the maintenance medium on production of HAV by this culture was examined. An incubation period of 24 to 28 days was found to be optimal; reducing this period led to decreased yields of HAV. No significant difference in the amount of HAV produced was observed with differing concentrations of fetal calf serum. Three different methods of extraction and the effect of multiple extractions on the recovery of HAV from cell lysates were examined. Sonication was a critical factor. Two extractions yielded more than 90% recoverable virus. Yields in excess of 10(11) physical particles of HAV per 850-cm2 roller bottle were routine. The total yield could be increased by concentrating the HAV present in spent maintenance medium by using bentonite or organic flocculation.     

Persistently infected cultures as a source of hepatitis A virus

Primary African green monkey kidney, continuous African green monkey kidney cell line BS-C-1, and buffalo green monkey kidney cultures were infected with a uniform inoculum of hepatitis A virus (HAV). Although both the cell line BS-C-1 and primary African green monkey kidney cultures produced useful amounts of virus, HAV was detected earlier and in greater quantities in primary African green monkey kidney cultures. A persistently infected primary African green monkey kidney culture was developed. The influence of incubation time (4 to 40 days) and concentration (2 to 15%) of fetal calf serum in the maintenance medium on production of HAV by this culture was examined. An incubation period of 24 to 28 days was found to be optimal; reducing this period led to decreased yields of HAV. No significant difference in the amount of HAV produced was observed with differing concentrations of fetal calf serum. Three different methods of extraction and the effect of multiple extractions on the recovery of HAV from cell lysates were examined. Sonication was a critical factor. Two extractions yielded more than 90% recoverable virus. Yields in excess of 10(11) physical particles of HAV per 850-cm2 roller bottle were routine. The total yield could be increased by concentrating the HAV present in spent maintenance medium by using bentonite or organic flocculation.     

Identification of functional murine adenosine deaminase cDNA clones by complementation in Escherichia coli

Total poly(A+) RNA derived from a mouse cell line with amplified adenosine deaminase genes was used as template to synthesize double-stranded cDNA. The cDNAs were inserted into the PstI site of the beta-lactamase gene in plasmid pBR322 following G-C tailing. After transformation into adenosine deaminase-deficient Escherichia coli hosts, recombinant plasmids containing functional murine adenosine deaminase cDNAs were identified by selecting for functional complementation. Analysis of plasmids containing functional adenosine deaminase cDNA sequences strongly suggested that adenosine deaminase expression resulted mainly from beta-lactamase/adenosine deaminase fusion proteins even when the adenosine deaminase codons were out-of-frame with respect to the beta-lactamase gene codons upstream. The nucleotide sequence of a 1.65-kilobase pair cDNA insert in one of the functional recombinant clones was determined and found to contain a 1056-nucleotide open reading frame. When this 1056-nucleotide open reading frame was inserted into a mammalian expression vector and introduced into monkey kidney cells, a high level of authentic mouse adenosine deaminase was produced. Nucleic acid blot analysis using a full-length adenosine deaminase cDNA clone as probe revealed that the mouse adenosine deaminase structural gene was at least 21 kilobase pairs in size and encoded three polyadenylated mRNAs. Analysis of the cDNA library from which the functional clones were isolated suggested that this approach of cloning functional mammalian adenosine deaminase cDNA clones by genetic complementation of enzyme-deficient bacteria could be accomplished even if the abundance of the adenosine deaminase mRNA sequences were as low as approximately 0.001%.     

Restriction map of the hepatitis B virus DNA cloned in Escherichia coli

A plasmid carrying the complete genome of hepatitis B virus (HBV) inserted into the BamHI site of the pBR322 plasmid vector has been constructed. The physical map of HBV DNA established for 13 restriction endonucleases allows to conclude that the cloned DNA is similar, but not identical to the HBV DNA of ayw subtype.