Influence of sequences in the long terminal repeat and flanking cell DNA on polyadenylation of retroviral transcripts

Readthrough transcripts are formed during retrovirus infection by polyadenylation of viral RNA in cellular sequences adjacent to the provirus. We have studied such transcripts in avian leukosis virus-infected cell clones containing a single provirus, either the wild type or one with an inactivating mutation in the poly(A) addition signal. All individual wild-type proviruses produced readthrough transcripts, implying that this property is not restricted to a few integration sites. The range of sizes of viral RNA in the mutant lacking a correct signal for poly(A) addition reflected both the occurrence of functional polyadenylation sites within flanking cell DNA and increased usage of cryptic sites within viral sequences.