RETROVIRUS RECOMBINATION DEPENDS ON THE LENGTH OF SEQUENCE IDENTITY AND IS NOT ERROR-PRONE

Retroviruses, as a result of the presence of two identical genomic RNA molecules in their virions, recombine at a high rate. When nonhomolog ous RNA is present in the dimer RNA molecules, nonhomologous recombina tion can occur, although the rate is very low, only 0.1% of the rate o f essentially homologous recombination (J. Zhang and H. M. Temin, Scie nce 259:234-238, 1993). We found, as is found in naturally occurring h ighly oncogenic retroviruses (J. Zhang and H. M. Temin, J. Virol. 67:1 747-1751, 1993), that the crossovers usually occur at a short region o f sequence identity. We modified the previously studied vectors to stu dy the effect of different lengths of short regions of sequence identi ty in the midst of otherwise nonidentical sequences. We found that the efficiency of recombination depends on the length of this sequence id entity. However, the highest rate in such molecules remained lower tha n for recombination between essentially homologous molecules, even whe n there was extensive sequence identity. Junction sequences of the rec ombinants indicated that retrovirus recombination is not an error-pron e process as was reported for human immunodeficiency virus reverse tra nscriptase by using a cell-free system (J. A. Peliska and S. J. Benkov ic, Science 258:1112-1118, 1992).