A defective retrovirus particle (SE21Q1b) packages and reverse transcribes cellular RNA, utilizing tRNA-like primers.

Linial and co-workers described a quail cell line, SE21Q1b, transformed by a single provirus of Rous sarcoma virus that is defective in virus assembly, in as much as the virus particles produced, SE21, contain cellular rather than viral RNA. In other respects these particles are normal, and the amount of endogenous DNA synthesis by disrupted virus particles is comparable to that of normal virus. We now report that endogenous DNA synthesis by SE21 virions uses RNA primers of the same size as tRNA species and that about 17% of these are bound to polyadenylate-containing RNA templates. Previous studies have shown that with wild-type Rous sarcoma virus, DNA synthesis is exclusively initiated on a tRNATrp species base paired to a specific location on the viral RNA. In contrast, we interpreted our data with SE21 as evidence that many different tRNA-primed initiations occurred, that predominantly species other than tRNATrp were used, and that the base pairing between template and primer RNAs included significant nucleotide mismatching. A subpopulation of the DNA synthesized by SE21 virions from tRNA-like primers was both initiated and terminated at discrete locations. These species are therefore analogous to the strong-stop DNA synthesized by wild-type virus.