The evolution of new species of viral DNA during serial passage of simian virus 40 at high multiplicity

Abstract

Viral DNA isolated during serial undiluted passage of SV40 was analysed by electrophoresis of fragments produced by H. influenzae restriction endonuclease and by DNA-DNA hybridization. Compared to parental SV40 DNA, early passage DNA showed alterations at many sites in the population of DNA molecules, although certain sites were more frequently altered than others as evidenced by the reduced yield of some original DNA fragments and the appearance of new fragments. With continued passage, new dominant species of viral DNA evolved which yielded simple restriction endonuclease digest patterns. DNA molecules from all passages retained SV40 DNA sequences; however, the percentage of total DNA sequences which corresponded to SV40 sequences diminished to about 30% or less in late passage DNA. Repetitive host cell DNA sequences were detected in a high percentage of late passage DNA molecules, but accounted for 20% or less of total sequences present. Therefore the new species of viral DNA which have evolved probably contain predominantly nonrepetitive host DNA sequences.