ELONGATION ACTIVITY OF POLIOVIRUS RNA-POLYMERASE DERIVED FROM SABIN TYPE-1 SEQUENCE IS NOT TEMPERATURE-SENSITIVE

Determinants of attenuation in the Sabin type 1 strain of poliovirus a re located in the 5' noncoding region, the capsid coding region and th e viral RNA-dependent RNA polymerase (3D(pol)) coding region. These mu tations also contribute to a temperature sensitive phenotype of virus replication. We have cloned and expressed the Sabin 1 virus 3D(pol) pr otein which contains three amino acid differences from the wild-type ( Mahoney) sequence, as well as a wild-type polymerase containing only a single Sabin amino acid substitution at nt 6203. These enzymes have b een examined and compared for temperature sensitive polymerase activit y. Wild-type and mutated polymerases demonstrated identical specific a ctivities at 30, 35 and 39 degrees C. All three showed the same kineti cs of heat inactivation after pre-incubation at elevated temperatures. Thus the contribution of Sabin 3D(pol) sequences to the inability of the virus to grow at elevated temperatures must lie in a function or a ctivity of the enzyme other than RNA polymerization. A likely reaction is the initiation step of RNA chain synthesis.