Potyviral HC-Pro: a multifunctional protein

Institut Jacques Monod, 2 place Jussieu - Tour 43, 75251 Paris Cedex 05, France Introduction. The genus Potyvirus , family Potyviridae , is the largest genus of plant viruses with 180 members or possible members (Brunt, 1992). Potyviruses are flexuous filamentous particles which contain a single-stranded RNA genome of positive polarity possessing a covalently linked 5'-terminal viral protein (VPg) and a 3'-terminal poly(A) tail (reviewed in Riechmann et al. , 1992). They are transmitted from plant to plant by aphids in a non-persistent manner, and this process is dependent on the presence of two virus-encoded proteins (reviewed in Pirone, 1991). One of these, the helper component-proteinase (HC-Pro) has attracted renewed attention during the last few years due to its multifunctionality and to it being implicated in different steps of the potyvirus life cycle. The properties, as well as the established and postulated functions of this protein, are reviewed.