Antibody to a host protein prevents initiation by the poliovirus replicase.

In vitro transcription of poliovirus RNA was catalyzed by the combination of a virus-coded polymerase and a host cell protein (host factor). Antibody to host factor inhibited template-dependent synthesis of complementary RNA where presumably RNA chain initiation occurred. On the contrary, elongation of already initiated RNA chains catalyzed by the replicase-template complex was not inhibited by anti-host factor antibody. These results strongly favored our previous notion that the host factor was needed for the initiation step of viral complementary RNA synthesis.