Comparison of two viable variants of simian virus 40

The DNAs of two viable strains of simian virus 40, 776 and 777, have been compared by using restriction endonucleases. Differences between the two strains were detected at five separate points on the simian virus 40 genome. One of these differences, in the region of DNA coding for the major viral coat protein, was confirmed by tryptic peptide analysis of coat proteins from the two strains. Some physiological differences between the two strains were examined and can, in general, be explained by differences observed between the DNAs of the two strains. In addition, defective variants derived from strain 777 interfere more efficiently with the replication of strain 777 than with the replication of strain 776.