There are several lines of evidence that both RNA
viruses and retroviruses recombine according to a copy
choice mechanism. Using the brome mosaic virus (BMV)-based
system, we recognized elements in the RNA structure that
enhance nonhomologous crossovers within or near the local
heteroduplex formed by recombining molecules. The same
structural motifs were employed in vitro to test the ability
of human immunodeficiency virus reverse transcriptase (HIV-RT)
to switch templates during DNA synthesis. We demonstrated
that a specific combination of the local double-stranded
region with short homologous sequences and a hairpin structure
allows template switching by HIV-RT. In contrast to BMV
replicase, HIV-RT does not mediate the detectable level
of recombination using only the heteroduplex structure,
though local hybridization between RNA molecules efficiently
pauses primer extension. Moreover, the presented data suggest
that a proper arrangement of identified structural motifs
can ensure site specificity of RNA–RNA recombination.
These results indicate that HIV-RT utilizes the same or
a very similar mechanism as BMV replicase to change nonhomologous
RNA templates in a site-specific manner.