Ribonucleic Acid Transcriptases in Sendai Virions and Infected Cells

Sendai virions contain an enzyme which catalyzes the incorporation of ribonucleotides into ribonucleic acid (RNA). Enzyme activity was optimal at pH 8.0 and 28 C; otherwise conditions were similar to those reported for Newcastle disease virion (NDV) RNA polymerase. The initial rate of RNA synthesis by the Sendai virion enzyme was about 10 pmoles per mg of protein per hr, but after 3 hr of incubation the rate increased about fivefold. The virion enzyme was compared with an RNA polymerase in the microsomal fraction of infected cells. Both enzymes made predominantly single-stranded RNA which was complementary in base sequences to 50S virion RNA. Most of the RNA synthesized by the virion polymerase sedimented at 16S, but the product of the microsomal enzyme sedimented at about 8S.