Abstract
It has previously been demonstrated that the DNA molecules containing a genetic marker from one region of a bacterial genome undergo complete strand separation at temperatures usually different from the molecules containing a genetic marker from another region of the genome. The experiments also showed that if a group of molecules undergo complete strand separation over a narrow temperature range, of the order of one to three degrees, it is highly likely that they all come from one region of the bacterial genome. The purpose of the work reported here was to establish appropriate procedures for doing a similar analysis of the DNA molecules containing the integrated SV40 DNA in transformed mouse cells. One result of interest is that in the 11A8 cell line about 40 per cent of the integrated SV40 DNA detectable by an RNA-DNA hybridization assay can be accounted for by a group of molecules which undergo complete strand separation within a 1.0 degree C interval.