Virus synthesis and replication: reovirus vs. vaccinia virus.

The strategies with which two viral genomes that consist of double-stranded nucleic acid express themselves in infected cells are compared. The reovirus genome comprises ten segments of double-stranded RNA, each of which is, in essence, a gene. Each is transcribed into plus-stranded RNA which has two functions: to serve as messenger RNA for the synthesis of the ten reovirus "primary" proteins, and to serve as template for the synthesis of minus-strands with which they remain associated, thereby giving rise to progeny double-stranded RNA. One of the most fascinating unsolved features of the reovirus multiplication cycle is the nature of the mechanism that ensures that each progeny virus particle contains a complete set of the ten individual genome RNA segments. The vaccinia virus genome is a linear molecule of double-stranded DNA which possesses sizable terminal redundancies (up to 7 percent, depending on the strain). The vaccinia virus multiplication cycle can be divided into a well-defined early and late period. During the early period, infecting virus particles are first uncoated to cores within which some 40-50 percent of the viral genome is transcribed. These cores are then uncoated further to naked viral DNA, a process that is mediated by protein(s) translated from the "core" messenger RNA. The overall transcription pattern in highly complex and is regulated both at the transcriptional as well as at the translational level. The most profound program changes occur at the time when DNA replication begins, when the transcription of "early" messenger RNAs, some of which are translated into "early" enzymes, gives way to that of "late" messenger RNAs, most of which are translated into structural virus components.