THE RECOMBINATION RATE IS NOT INCREASED WHEN RETROVIRAL RNA IS MISSING AN ENCAPSIDATION SEQUENCE

Retroviruses, as a result of the presence of two identical RNA molecul es in their virions, recombine at a high rate, When nonhomologous RNA is present in the dimer RNA molecules, nonhomologous recombination occ urs, although the rate is only 0.1% of the rate of homologous recombin ation. We developed a protocol to study transduction of cellular proto -oncogenes in a single cycle of retrovirus replication. The Psi sequen ce is a cis required sequence for packaging viral RNA into viral parti cles. To test if the rate of nonhomologous recombination increases abo ut 1,000 times when the Psi sequence is deleted, as reported by others , we modified vectors we used previously (J. Zhang and H. M. Temin, Sc ience 259:234-238, 1993). Our result indicated that the recombination rate did not undergo the increase of about 1,000 times when the Psi se quence of a chimeric RNA was deleted.