The structure of a cloned substituted SV40 genome

The structure of the DNA of a cloned host-substituted SV40 variant was investigated by restriction endonuclease cleavage mapping and hybridization of the cleavage products to monkey and wild-type SV40 DNAs. The circular DNA of this variant was shown to consist of four tandemly repeated segments, each of which consists of covalently linked viral and monkey DNA sequences. Only two of the repeated subunits are of equal size. A detailed cleavage map of the variant genome is presented. The viral sequences in each of the four subunits are derived from within a portion of the wild-type SV40 genome (0.59-0.73 map units), which contains the origin of replication. Monkey DNA sequences of the reiterated type are linked to monkey DNA sequences of the less-reiterated or nonreiterated type in three of the subunits. The monkey DNA sequences in the fourth subunit are predominantly of the reiterated type. Hybridization experiments to clarify the relationship between the host DNA sequences in the cloned variant and those in other independently derived substituted SV40 populations indicate that some populations share some of the same reiterated and nonreiterated host DNA sequences, whereas other populations share only the reiterated host DNA sequences.