Rl. Gladding et al., EVALUATION OF THE SUSCEPTIBILITY OF THE 3C PROTEASES OF HEPATITIS-A VIRUS AND POLIOVIRUS TO DEGRADATION BY THE UBIQUITIN-MEDIATED PROTEOLYTIC SYSTEM, Biochemical and biophysical research communications, 238(1), 1997, pp. 119-125
The picornavirus 3C proteases are required for the processing of viral
polyproteins during infections of host cells. Here we report that the
3C protease of the hepatitis A virus, like that of the encephalomyoca
rditis virus, is a substrate for rapid, ubiquitin-mediated degradation
in vitro. Ubiquitin was shown to stimulate the turnover of the hepati
tis virus 3C protease, and labeled protease was found to become incorp
orated into a mixture of high molecular weight species, which is chara
cteristic of conjugation with polyubiquitin chains. In the presence of
methylated ubiquitin, a new 33 kDa species formed, consistent with th
e generation of a monoubiquitin-3C protease conjugate. The rate of deg
radation of the 3C protease was reduced by inhibitors of the 26S prote
asome. A similar evaluation of the 3C protease of poliovirus revealed
that it is stable protein and is not conjugated with ubiquitin. It was
also determined that the hepatitis A and encephalomyocarditis virus 3
C proteases compete with each other for conjugation with ubiquitin and
for degradation. This suggests that the two 3C proteases are both rec
ognized by the same ubiquitin system enzyme, or enzymes, responsible f
or selecting them as targets for destruction. (C) 1997 Academic Press.