Isolation of nucleic acid-binding protein: stimulation of reverse transcriptase-catalysed DNA synthesis

Abstract

RNA tumour viruses transfer their genetic information from a single-stranded RNA genome found in their virions to a double-stranded DNA covalently integrated into chromosomes of the infected host^1,2. A series of nucleic acid intermediates must therefore exist between the single-stranded RNA and the integrated viral DNA genome. The discovery of RNA-directed DNA polymerase (reverse transscriptase) associated with RNA tumour viruses fulfilled a critical requirement for synthesis of viral DNA^3,4. The initial product in this information transfer is a RNA–DNA hybrid which is converted into free, unintegrated DNA–DNA^5,6. The double-stranded DNA (provirus) is then integrated into chromosomes of the infected host. We report here the isolation of a nucleic acid-binding (unwinding) protein from chick fibroblasts transformed by Rous sarcoma virus (RSV) and its stimulatory effect on DNA synthesis catalysed by reverse transcriptase. A protein capable of unwinding RNA–DNA hybrid and DNA–DNA duplex would not only conserve the input viral RNA strand for further reverse transcription, but also facilitate replication of the double-stranded viral DNA into many copies of provirus before integration.