Repair of ultraviolet light damage in Saccharomyces cerevisiae as studied with double- and single-stranded incoming DNAs.

Purified double- and single-stranded DNAs of the autonomously replicating vector M13RK9-T were irradiated with ultraviolet light (UV) in vitro and introduced into competent whole cells of Saccharomyces cerevisiae. Incoming double-stranded DNA was more sensitive to UV in excision repair-deficient rad2-1 cells than in proficient repair RAD+ cells, while single-stranded DNA exhibited high sensitivity in both host cells. The results indicate that in yeast there is no effective rescue of UV-incoming single-stranded DNA by excision repair or other constitutive dark repair processes.