Efficient packaging of readthrough RNA in ALV: implications for oncogene transduction.

Readthrough viral transcripts are present at relatively high levels in cells infected with avian leukosis virus. It has been proposed that they can function as intermediates in the transduction of proto-oncogenes by retroviruses. It is shown here, by the analysis of viruses containing a mutation in the AAUAAA polyadenylation signal, that readthrough RNAs have the requisite properties to function as transduction intermediates: readthrough RNAs were polyadenylated and packaged as efficiently as normal viral RNA, RNAs nearly 11.2 kilobases (3.5 kilobases larger than wild-type avian leukosis virus genomes) were present in virions of the mutant virus, and virus particles containing both readthrough and normal genomes were most likely infectious.