Terminal redundancy and the origin of replication of Rous sarcoma virus RNA.

In vitro synthesis of Rous sarcoma virus DNA by the virion endogenous DNA polymerase activity is initiated on a tRNAtrp primer located near the 5' end of the genome. A major product of such synthesis is a piece of DNA 101 nucleotides long (strong stop DNA) which can be isolated covalently bound to the tRNA primer. Here we show that the strong stop DNA is complementary to the extreme 5' end of the genome. We also show that the 5' and 3' termini of the Rous sarcoma virus genome, excluding the cap and the poly(A), have the identical sequence. We propose that the function of this sequence is to facilitate elongation from the 3' end of DNA chains initiated elsewhere on the virus genome.