In Vivo Excision of Pyrimidine Dimers Is Mediated by a Dna N‐glycosylase in Micrococcus Luteus but Not in Human Fibroblasts

It has been previously shown that Micrococcus luteus possesses a pyrimidine dimer‐specific endonuclease which in vitro , functions as both an endonuclease and DNA‐glycosylase. To determine if these combined activities function in vivo , we have isolated and examined the excision products of UV‐irradiated M. luteus . In addition, we have devised a procedure to isolate and examine the excision products from UV‐irradiated human fibroblasts to determine if an endonuclease/glycosylase activity functions in the excision of UV‐induced pyrimidine dimers in human fibroblasts. We find that, in vivo , an endonuclease/glycosylase mechanism is utilized extensively in the repair of pyrimidine dimers by M. luteus , but that human fibroblasts do not appear to use this mechanism.