REPLICATION OF AVIAN-LEUKOSIS VIRUSES WITH MUTATIONS AT THE PRIMER BINDING-SITE - USE OF ALTERNATIVE TRANSFER-RNAS AS PRIMERS

We have tested whether avian leukosis viruses (ALVs) can use tRNAs oth er than tRNA(Trp) to initiate reverse transcription, The primer bindin g site (PBS) of a wild-type ALV provirus, which is complementary to th e 3' end of tRNA(Trp), was replaced with sequences homologous to the 3 ' ends of six different chicken tRNAs (tRNA(Pro) tRNA(Lys), tRNA(Met), tRNA(Ile), tRNA(Phe), and tRNA(Ser)). Transfection of these proviruse s into chicken embryo fibroblasts resulted in the production of infect ious viruses, all of which apparently used the tRNA specified by the m utated PBS to replicate. However, growth of these viruses resulted in reversion to the wild-type (tRNA(Trp)) PBS. Some of the viruses revert quite quickly, while others are more stable. The relative stability o f, a given PBS correlated with the concentration of the corresponding tRNA in the virion. We determined the percentage of viral RNA that had a tRNA bound to the PBS and found that the occupancy rate is lower in the mutants than in the wild-type virus. We conclude that;many differ ent tRNAs can be used as primers to initiate reverse transcription in ALV. However, ALVs that use tRNA(Trp) have a growth advantage over ALV s that use other tRNAs.