Nuclear conversion of microinjected avian leukosis virion RNA into an envelope-glycoprotein messenger

Abstract

IN eukaryotes, cellular^1–4 as well as viral^5–7 messenger RNA molecules may contain nucleotide sequences complementary to discontinuous regions of DNA. This is apparently the case with subgenomic avian RNA tumour virus mRNAs. In these viruses the entire genetic information is contained on a 30–40S^8,9 virion RNA molecule which is transcribed from a DNA provirus integrated into the host chromosomes¹⁰. Subgenomic viral mRNAs contain only genes located in the 3′ half of the virion molecule^11–15, but contain 5′ terminal nucleotide sequences (ref. 13; W. S. Hayward and W. Haseltine, personal communication) and oligonucleotides¹⁶ apparently identical to those at the 5′ terminus of the larger virion molecule. As has been suggested for other mRNAs, subgenomic RNA tumour virus mRNAs might be derived from a larger precursor¹⁷ by processing involving cleavage and subsequent ligation, resulting in the elimination of internal nucleotides from the precursor^5,18. The data do not rule out the possibility, however, that subgenomic mRNAs are produced by transcription of discontinuous DNA sequences within the integrated provirus; or even that they result from transcription of a subgenomic provirus. The biological experiments reported here support the hypothesis that the envelope-glycoprotein messenger of the avian leukosis virus RAV-2 (Rous associated virus-2) can be derived from a larger precursor, and indicate that the virion RNA itself can function as the precursor.