Complementation between SV40 and RFV defectives and acquisition of SV40 origins by late RFV genomes

EL SV40 and RFV are variants of SV40 and BKV which contain bipartite or dual genomes. One molecule contains all the early viral sequences (E-SV40, E-RFV) and the other all the late viral sequences (L-SV40, L-RFV). Early and late genomes complement one another during productive infection. Experiments were designed to determine if E-genomes of one virus could complement L-genomes of another virus. If complementation did occur, intermolecular recombination events which lead to a more efficient infection or an altered host range might occur, and the sequences involved could than be identified. Two combinations were generated by direct transfection of BSC-1 green monkey cells. E-RFV and L-SV40 DNA complementation resulted in hybrid virus growth and cell killing. The hybrid demonstrated a narrow host range. Following serial passage, some E-RFV genomes contained SV40 origin region sequences but these recombinants did not overgrow prototype E-RFV genomes, even after many virus passages. In addition, no significant alterations in host range could be detected. Complementation between E-SV40 and L-RFV yielded a virus with a relatively wider host range. Virus growth and cell killing appeared very slowly at first. However, with each passage of E-SV40/L-RFV, cell killing occurred progressively more rapidly, until passage 7 when it became extensive in 7 days rather than 6-8 weeks. Infected cells contained 10-20 times more E-SV40 than L-RFV DNA during the first passage. However, by passage 7, both genomes were equally represented. During serial passage, L-RFV DNA acquired SV40 sequences from around the origin and the terminus of replication, such that recombinant (r) L-RFV genomes contained three SV40 origins [corrected] (including the 72-bp repeat) and 2 termini, and prototype L-RFV DNA was lost. E-SV40/rL-RFV demonstrated an altered host range propagating in some cell lines which did not support E-SV40/L-RFV growth. Both the host range change and the increased growth of rL-RFV genomes were shown to be at least partly caused by the acquisition of the SV40 sequences.