In HeLa cells, RNA polymerase II mediated transcription is severely in
hibited by poliovirus infection. Both basal and activated transcriptio
n are affected to bring about a complete shutoff of host cell transcri
ption. We demonstrate here that the octamer binding transcription fact
or, Oct-1, is cleaved in HeLa cells infected with poliovirus. Incubati
on of Oct-1 with the purified, recombinant 3C(pro) results in the gene
ration of the cleaved Oct-1 product seen in virus infected cells. Poli
ovirus infection leads to the formation of altered Oct-1-DNA complexes
that can also be generated by incubation of Oct-1 with purified 3C(pr
o). We also show that Oct-1 cleaved by 3C(pro) loses its ability to in
hibit transcriptional activation by the SV40 B enhancer. These results
suggest that cleavage of Oct-1 in poliovirus infected cells leads to
the loss of its activity. (C) 1997 Academic Press.