Plant Virus Proteinases 235product but also regulate its activity or subcellular localization by removal of functional domains.Genes of alphalike, carmolike, and sobemolike viruses are expressed through different combinations of strategies acting at the level of transcription (synthesis of subgenomic (sg) RNAs) and/or translation (alternative translation initiation sites, frameshifting, and readthrough at suppressible termination codons). In some cases, gene expression is completed posttranslationally by proteolysis mediated by a virus-encoded proteinase.Proteolytic processing of protein precursors has also been observed in plant pararetroviruses. These viruses have double-stranded (ds) DNA genomes that replicate via RNA intermediates (Hohn and FOtterer, 1997). In this case, the virus-encoded proteinase belongs to the aspartic family and a host cysteine proteinase seems to be involved in the maturation of a viral protein.Here, we have attempted to give an overall view of the use of proteolytic processing by different plant virus groups for the expression of their genomes.