HIGH-RATE OF MISMATCH EXTENSION DURING REVERSE TRANSCRIPTION IN A SINGLE ROUND OF RETROVIRUS REPLICATION

We made spleen necrosis virus-based retroviral vectors with mutations at the 3' end of the primer binding site region to observe the effects of terminal mismatches on retroviral replication. These vectors, when compared to a vector with the wild-type primer binding sequence, allo wed us to assay the effects of the mutations on the viral titer during a single cycle of replication. The mutant vectors had titers that wer e comparable to the wild-type vector, indicating that reverse transcri ptase has no trouble extending mismatches of as many as 3 bases under normal in vivo conditions. These results confirm and extend previous i n vitro studies [Yu, H. and Goodman, M. (1992) J. Biol. Chem. 15, 1088 8-10896] that showed that such mismatch extension could occur in a cel l-free system at high concentrations of incorrect nucleotides and in t he absence of correct nucleotides. We now show that mismatch extension can occur during normal retroviral replication in cells and at normal physiological nucleotide concentrations.