Induction of sister chromatid exchanges by transformation with simian virus 40

The frequency of sister chromatid exchange (SCE) has been followed sequentially after the addition of SV40 to human diploid fibroblast cultures. The SCE frequency was nearly the same in uninfected controls and in infected cultures before they became tumor antigen positive. When cells exhibited tumor antigen, the SCE frequency increased over a wide range, and changes in chromosome number and structure were observed simultaneously. Cells with induced chromosome abnormalities without increased SCE's and the reverse present the possibility that the two phenomena have different viral mechanisms. This increase in SCE can be added to the previously demonstrated change in chromosome number and increase in chromosome breakage and rearrangement as indicators of genetic damage associated with viral transformation.