clone 707 wild-type cells in the presence of caffeine could then continue to repair dna damage through an intact though less effective excision repair system , whilst the thymidine kinase-deficient subclone 707buf would , in the presence of caffeine , be rendered highly mutagen sensitive , being only able to repair dna damage through an error-prone excision repair process .
C0012860
dna
C0012899
dna