Homologous recombination of a plasmid containing the SV40 early region in rabbit cells.

The plasmid pSV3-neo that carries the SV40 early genetic region and the neor resistance gene underwent homologous recombination between SV40-duplicated sequences of the small t antigen intron and the polyadenylation site after transfection into rabbit vascular smooth muscle cells. This recombination yielded two free plasmids of 1.7 and 3.0 kb that replicated in transfected rabbit cells, while the vector plasmid did not. Replication of the two recombinant plasmids continued for several months in rabbit cells transformed by pSV3-neo, and their structure remained unchanged. Between 15 and 2,510 copies per cell of the 3.0-kb plasmid and between 370 and 1,565 copies per cell of the 1.7-kb plasmid were found in different pSV3-neo-transformed rabbit clones. Similar recombined plasmids were found 3 days after transfection of pSV3-neo onto SV40-transformed rabbit cells. By comparison, pSV3-neo was replicated in simian cells, but no recombined plasmids were detected by Southern analysis. No replication was detected after transfection of pSV3-neo into mouse cells. These results appear to reflect important differences between rabbit and simian cells in the efficiency of homologous recombination involving specific SV40 sequences and/or in the replication of the resulting recombinants. The role of the host cell in the evolution of SV40 sequences may influence the outcome of the infection with this virus.