Extensive reverse transcription of RSV genome by nucleic acid-binding protein

Abstract

THE discovery of reverse transcriptase^1,2 offered the possibility of using in vitro synthesis to study the replication of RNA tumour virus genomes in molecular detail. Attempts to study DNA provirus formation in vitro, however, have encountered serious obstacles: poor efficiency of transcription, small DNA products, and unequal representation of the viral RNA sequences in the DNA product have been common findings³. These difficulties in copying RNA into DNA have led to suggestions that cellular factors, such as ligases or unwinding proteins might be necessary to assist reverse transcriptase in copying the viral RNA genome into a complete DNA transcript^4,5. Binding (unwinding) proteins involved in DNA synthesis are well known in bacteria^6,7 and have also been described in mammalian systems⁸. We reported previously the isolation of a DNA binding protein from transformed chicken cells and its stimulating effect on reverse transcriptase activities⁵. Here we present evidence that, in the presence of the binding protein, purified reverse transcriptase from Rous sarcoma virus (RSV) synthesised an extensive, possibly complete complementary transcript of DNA from the viral RNA genome in a totally reconstituted reaction system.