M. Nacht et al., SIMIAN-VIRUS-40 LARGE T-ANTIGEN AFFECTS THE SACCHAROMYCES-CEREVISIAE CELL-CYCLE AND INTERACTS WITH P34(CDC28), Journal of virology, 69(2), 1995, pp. 756-763
Simian virus 40 tumor (T) antigen, an established viral oncoprotein, c
auses alterations in cell growth control through interacting with, and
altering the function of, cellular proteins. To examine the effects o
f T antigen on cell growth control, and to identify the cellular prote
ins with which it may functionally interact, T antigen was expressed i
n the budding yeast Saccharomyces cerevisiae. The yeast cells expressi
ng T antigen showed morphological alterations as well as growth inhibi
tion attributable, at least in part, to a lag in progression from G(1)
to S. This point in the cell cycle is also known to be affected by T
antigen in mammalian cells. Both p34(CDC28) and p34(CDC2Hs) were shown
to bind to a chimeric T antigen-glutathione S-transferase fusion prot
ein, indicating that T antigen interacts directly with cell cycle prot
eins which control the G(1) to S transition. This interaction was conf
irmed by in vivo cross-linking experiments, in which T antigen and p34
(CDC28) were coimmunoprecipitated from extracts of T-antigen-expressin
g yeast cells. These immunoprecipitated complexes could phosphorylate
histone H1, indicating that kinase activity was retained. In addition,
in autophosphorylation reactions, the complexes phosphorylated a nove
l 60-kDa protein which appeared to be underphosphorylated (or underrep
resented) in p34(CDC28)-containing complexes from cells which did not
express T antigen. These results suggest that T antigen interacts with
p34(CDC28) and alters the kinase function of p34(CDC28)-containing co
mplexes. These events correlate with alterations in the yeast cell cyc
le at the G(1) to S transition.