Replication and pathogenicity of primer binding site mutants of SL3-3 murine leukemia viruses

Retroviral reverse transcription is primed by a cellular tRNA molecule anne aled to an 18-bp primer binding site sequence. The sequence of the primer b inding site coincides with that of it negatively acting cis element that me diates transcriptional silencing of murine leukemia virus (MLV) in undiffer entiated embryonic cells. In this study we test whether SL3-3 MLV can repli cate stably using tRNA primers other than the cognate tRNA(Pro) and analyze the effect of altering the primer binding site sequence to match the 3' en d of tRNA(1)(Gln), tRNA(3)(Lys), or tRNA(1,2)(Arg) in a mouse pathogenicity model. Contrary to findings from cell culture studies of primer binding si te-modified human immunodeficiency virus type 1 and avian retroviruses, our findings were that SL3-3 MLV may stably and efficiently replicate with tRN A primers other than tRNA(Pro). Although lymphoma induction of the SL3-3 Ly s3 mutant was significantly delayed relative to that of the wild-type virus , molecular tumor analysis indicated that all the primer binding site-modif ied viruses induce T-cell lymphomas similar to those induced by the wild-ty pe virus in terms of frequencies of genomic rearrangements within the T-cel l receptor beta-chain, the immunoglobulin kappa light chain, and the c-myc locus. Whereas none of the mutants were found to revert to tRNA(Pro) primer utilization, in two tumors resulting from the injection of the SL3-3 Lys3 mutant the primer binding site was altered to match that of a new primer sp ecies, tRNA(1,2)(Lys). In addition, recombination with endogenous viruses r esulting in the generation of recombinant viruses carrying a glutamine prim er binding site was detected in the majority of the tumors induced by the S L3-3 Lys3 mutant as well as in two tumors induced by wild-type SL3-3 and th e SL3-3 Arg1,2 mutant.