Restoration of preferential and strand specific gene repair in group 2 Chinese hamster ovary mutants (UV5) by the XPD (ERCC2) gene.

It has recently been reported that the XPD (ERCC2) gene is an integral component of the basal transcription factor TFIIH. We have studied the direct role of this repair gene on the fine structure of DNA repair in hamster cells. The gene and strand specific DNA repair of UV induced pyrimidine dimers was determined in wild-type hamster cells, in hamster cells harboring a mutation in the gene homologous to the XPD gene and in mutant cells transfected with the human XPD gene. In the mutant cells, strand specific repair was severely deficient. In the transfected cells, preferential and strand specific gene repair were restored to wild-type levels. The results of the current study clearly demonstrate a direct role for the XPD gene product both in the preferential repair and bulk repair of pyrimidine dimers as well as its high functional conservation between rodent and human cells. An in vitro transcription assay was employed to investigate whether RNA polymerase II mediated transcription was also affected by the transfection with the XPD gene. No change in transcription between the mutant and transfected cells was observed. This suggests that the role of XPD in repair can be distinguished from its role in TFIIH dependent transcription initiation. Different functional domains of XPD appear to be necessary for repair versus transcription.