Genetic effects of formaldehyde in yeast. II. Influence of ploidly and of mutations affecting radiosensitivity on its lethal effect.

Haploid and diploid cells of Saccharomyces cerevisiae have the same sensitivity to formaldehyde, exponentially growing cells being more sensitive than stationary phase cells for both degrees of ploidy. Strains defective (rad 1-3) or with a reduced capacity (p-, cytoplasmic respiratory deficient mutants) in excision repair of ultraviolet-induced pyrimidine dimers show a greater sensitivity to formaldehyde than the corresponding wild type. A mutant defective in radiation-induced gene conversion (rec5) shows the same sensitivity as the wild-type strain. It appears that the excision-repair system plays an important role, especially in stationary phase cells, in repairing a fraction of formaldehyde-induced lesions.