Chang L J, Pryciak P, Ganem D, Varmus H E
Department of Microbiology and Immunology, University of California Medical Center, San Francisco 94143.
Nature. 1989 Jan 26;337(6205):364-8. doi: 10.1038/337364a0.
Retroviruses and many other types of genetic elements replicate by reverse transcription of RNA. Although structurally and biologically very diverse, such elements carry conserved polymerase genes (pol) that encode proteins required for reverse transcription. In most cases, the pol gene is preceded by an overlapping gene encoding one or more nucleocapsid proteins, in a different reading frame. Because both coding regions are represented in a single mRNA, the question arises of how the reverse transcriptase in the alternative reading frame is expressed. In retroviruses and retrotransposons it is expressed as a nucleocapsid-polymerase fusion protein by ribosomal frameshifting during translation of the overlapping region. We have examined the mechanism of polymerase biosynthesis in another family of animal viruses that use reverse transcription, the hepatitis B viruses. Genetic and biochemical studies reveal that these viruses do not use ribosomal frameshifting to generate this enzyme, but instead direct translation initiation at an internal initiation (AUG) codon in the polymerase gene.
逆转录病毒和许多其他类型的遗传元件通过RNA的逆转录进行复制。尽管这些元件在结构和生物学特性上差异很大，但它们都携带保守的聚合酶基因（pol），该基因编码逆转录所需的蛋白质。在大多数情况下，pol基因之前是一个重叠基因，该重叠基因以不同的阅读框编码一种或多种核衣壳蛋白。由于两个编码区域都存在于单个mRNA中，因此就出现了一个问题，即在不同阅读框中的逆转录酶是如何表达的。在逆转录病毒和逆转座子中，它是在重叠区域翻译过程中通过核糖体移码表达为核衣壳 - 聚合酶融合蛋白的。我们研究了另一类使用逆转录的动物病毒——乙型肝炎病毒中聚合酶生物合成的机制。遗传和生化研究表明，这些病毒不使用核糖体移码来产生这种酶，而是在聚合酶基因的内部起始（AUG）密码子处直接进行翻译起始。
