Ds. Lyles et al., POTENCY OF WILD-TYPE AND TEMPERATURE-SENSITIVE VESICULAR STOMATITIS-VIRUS MATRIX PROTEIN IN THE INHIBITION OF HOST-DIRECTED GENE-EXPRESSION, Virology, 225(1), 1996, pp. 172-180
The matrix (M) protein of vesicular stomatitis virus (VSV) functions i
n virus assembly and also appears to be involved in the inhibition of
host gene expression that is a characteristic cytopathic effect of VSV
infection. Previous studies have shown that expression of M protein i
nhibits host-directed transcription in the absence of other viral gene
products and have suggested that only small amounts of M protein are
required for the inhibition. In experiments described here, the potenc
y of M protein in inhibition of host-directed gene expression was dete
rmined by cotransfecting different amounts of in vitro-transcribed M p
rotein mRNA together with a target gene encoding chloramphenicol acety
l transferase (CAT) into BHK cells or PC12 cells that had been culture
d in the presence or the absence of nerve growth factor. The results o
f these experiments showed that the potency of M protein was similar i
n the two cell types and was not affected by the extent of differentia
tion of PC12 cells. Inhibition of CAT gene expression by M protein was
also independent of the nature of the promoter activating sequences o
f several different RNA polymerase Ii-dependent promoters. The amount
of M protein needed to give 50% inhibition of CAT expression was estim
ated to be 6700-11,000 copies per cell. Earlier data that temperature-
sensitive (ts) M gene mutants of VSV inhibit host transcription had be
en interpreted to indicate that M protein was not involved in the inhi
bition. When the amount of M protein expressed was taken into account,
ts M protein was as effective as wild-type M protein in the inhibitio
n of host-directed transcription at the nonpermissive temperature Thus
, inhibition of host transcription by ts M mutants of VSV is due to th
e potent activity of M protein, which is evident even at the low level
s produced at the nonpermissive temperature (C) 1996 Academic Press, I
nc.