Stable polypeptides associated with the 250S mengovirus-induced RNA polymerase structure.

One host polypeptide (40,000 daltons) synthesized prior to infection is associated with the 250S RNA polymerase structure partially purified by a combination of velocity sedimentation and isopycnic separation. A series of pulse-chase experiments have shown that a 56,000 dalton polypeptide made during the eclipse phase of infection is inserted into the 250S viral RNA polymerase structure. This 56,000 dalton polypeptide is bound in a stable manner since labeled 56,000 dalton polypeptide is not removed from the 250S polymerase structure by a 2-hour chase (3 to 5 hours after infection) and it is the major labeled polypeptide species remaining. However, the 56,000 dalton polypeptide (viral-specific polypeptide E) made at 4 hours after infection is not present in the 250S polymerase structure following a 50 minue chase. Levels of cycloheximide which inhibit protein synthesis 95 per cent in the infected cell have no effect on the amount of viral-specific RNA polymerase activity (in vitro) when the inhibitor is added for 30 minutes at the time of maximum rate of viral RNA synthesis in whole cells. These inhibitor studies support the hypothesis that the viral-specific RNA polymerase polypeptide may be a stable polypeptide that is not rapidly turning over in the infected cell. In view of these results the stable 56,000 dalton polypeptide (polypeptide E) made early in infection may be a candidate for the viral-specific polymerase polypeptide.