Transcription of DNA from the 70 S RNA of Rous Sarcoma Virus II. Structure of a 4 S RNA Primer

Abstract

The 70 S RNA of Rous sarcoma virus contains 4 S RNAs which serve as primers for the initiation of DNA synthesis in vitro by the RNA-directed DNA polymerase of the virus. We purified these primers in three different ways—by isolation of the covalent complex between primer and nascent DNA, by differential melting of the 70 S RNA, and by two-dimensional electrophoresis in polyacrylamide gels. The 4 S RNAs purified by these procedures were homogeneous and possessed very similar if not identical nucleotide compositions and sequences. The RNAs were approximately 75 nucleotides long, had pG at the 5′ terminus and CpCpA OH at the 3′ terminus, and contained a number of minor nucleotides characteristic of tRNA. In contrast to most tRNA's, the primer lacked rTp and contained Gp (Ψp, Ψp, Cp) Gp (possibly in place of the characteristic sequence GprTpΨpCpGp). At least 50% of the 4 S primers available on 70 S RNA were utilized in a standard polymerase reaction in vitro.