R. Margis et al., DIFFERENTIAL PROTEOLYTIC ACTIVITIES OF PRECURSOR AND MATURE FORMS OF THE 24K PROTEINASE OF GRAPEVINE FANLEAF NEPOVIRUS, Virology, 200(1), 1994, pp. 79-86
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.