Small plaque variants of simian virus 40 from a persistent infection of rhesus monkey kidney cells.

Seven small-plaque variants from a simian virus 40-rhesus monkey kidney cell carrier system were compared with the standard large plaque strain by restriction endonuclease analysis. One of these variants, SP1, contains an insertion of about 50 base pairs between the Bgl1 (map location 0.67) and Hpa11(0.73) cleavage sites. Another, SSP2, contains a deletion of about six base pairs in Hind 11 + 111 fragment K. The rates of replication and release of both SP1 and SP2 are similar to that of wild-type virus at 37°, although SP1 is slightly temperature sensitive at 41° and SP2 is slightly cold sensitive at 33°. Both SP1 and SP2 effectively compete with wild-type virus at 37° under conditions of mixed infection. Competition by SP1 is expressed, at least in part, at the level of DNA synthesis.