A guanidine-sensitive step of the poliovirus RNA replication cycle.

It has been shown that the amount of viral RNA synthesized in synchronized HeLa cells 0-2 h after infection does not notably vary during the mitotic cycle. However, the amount of viral RNA synthesized 2-4.5 h after infection exhibited a sharp maximum in S-phase cells. Guanidine inhibited the incorporation of 3-H-uridine into the viral RNA synthesized 2-4.5 h after infection only in cells in the S-phase. It had no demonstrable effect on viral RNA synthesis 0-2 h after infection in cells in any phase of the mitotic cycle. Thus, additional indirect evidence has been presented in favor of the hypothesis that two different replicases or two different conformations of one enzyme are involved in poliovirus RNA replication. The one functioning 0-2 h after infection is cycle-independent and guanidine-sensitive, whereas the other functions exclusively in phase-S cells 2-4.5 h after infection and is inhibited by guanidine.