EXPRESSION OF VIRUS-ENCODED PROTEINASES - FUNCTIONAL AND STRUCTURAL SIMILARITIES WITH CELLULAR ENZYMES

Many viruses express their genome, or part of their genome, initially as a polyprotein precursor that undergoes proteolytic processing. Mole cular genetic analyses of viral gene expression have revealed that man y of these processing events are mediated by virus-encoded proteinases . Biochemical activity studies and structural analyses of these viral enzymes reveal that they have remarkable similarities to cellular prot einases. However, the viral proteinases have evolved unique features t hat permit them to function in a cellular environment. In this article , the current status of plant and animal virus proteinases is describe d along with their role in the viral replication cycle. The reactions catalyzed by viral proteinases are not simple enzyme-substrate interac tions; rather, the processing steps are highly regulated, are coordina ted with other viral processes, and frequently involve the participati on of other factors.