REGULATION OF VACCINIA VIRUS GENE EXPRESSION AND DNA REPLICATION

痘病毒在受感染细胞的细胞质中编码转录和复制其基因组所需的酶和因子。痘苗病毒是痘病毒家族的原型成员，为研究基因调控、mRNA生物合成和DNA复制机制提供了一个独特的生物化学和遗传方法相结合的系统。对牛痘病毒的研究表明，这些基因在时间上可分为早期、中期和晚期三种类型。每个基因类都有一个一致的DNA启动子序列和相应的转录因子，这些转录因子与病毒编码的多亚基RNA聚合酶相互作用。早期基因转录系统在感染病毒颗粒组装时被包装在其内部，而中、晚期基因转录因子则在感染后陆续合成。DNA被合成为串联体，在病毒组装过程中被分解成单位长度的基因组和包装。

Poxviruses encode enzymes and factors needed for transcription and replication of their genomes within the cytoplasm of infected cells. Vaccinia virus, the prototypic member of the poxvirus family, provides a unique system for combining biochemical and genetic approaches for investigating mechanisms of gene regulation, mRNA biosynthesis, and DNA replication. Studies with vaccinia virus indicated that the genes are divided into three temporal classes - early, intermediate and late. Each gene class has a consensus DNA promoter sequence and corresponding transcription factors that interact with the virus-encoded multisubunit RNA polymerase. The transcription system for early genes is packaged within the infectious virus particle during its assembly, whereas the factors for intermediate and late gene transcription are synthesized successively after infection. The DNA is synthesized as concatemers that are resolved into unit length genomes and packaged during virus assembly.