DIFFERENTIAL PROTEOLYTIC ACTIVITIES OF PRECURSOR AND MATURE FORMS OF THE 24K PROTEINASE OF GRAPEVINE FANLEAF NEPOVIRUS

The presence of a genome-linked protein (VPg) at the RNA B-end of the genome is a characteristic of different groups of animal and plant pos itive-sense single-stranded RNA viruses. These viruses express their s tructural and functional proteins from polyproteins that are sequentia lly processed by at least one viral proteinase. The grapevine fanleaf nepovirus 24K chymotrypsin-like cysteine proteinase, located between t he VPg and the RNA polymerase in the RNA-1 encoded polyprotein P1, is active in its free form and in various precursors forms. The VPS prote inase precursor (VPg-Pro) constitutes a stable protein and its maturat ion in the reticulocyte lysate system occurs at a very low rate. Diffe rences on cleavage activity were observed between the proteinase and i ts VPg-Pro precursor forms, depending upon the cleavage site considere d. The proteinase alone has a greater cleavage efficiency than VPg-Pro at the Arg(605)/Gly(606) and Cys(257)/Ala(258) sites of polyprotein P 2. On the other hand, the presumed Cys(415)/Ala(416) site, present at the amino terminus of polyprotein P1, was preferentially cleaved by th e VPg-Pro precursor. During their in vitro maturation, proteins contai ning the VPg proteinase-polymerase coding region or the proteinase-pol ymerase region were similar in their ability to cleave in cis between the proteinase and the RNA polymerase. (C) 1994 Academic Press, Inc.