Genetic effects of formaldehyde in yeast. III. Nuclear and cytoplasmic mutagenic effects.

Low concentrations of formaldehyde induce nuclear mutations when yeast cells are allowed to grow in the presence of this compound. The induction of reversions is a linear function of the concentration and depends upon the repair capacities of the treated cells. A strain defective in excision-repair (rad3-12) is more mutable by formaldehyde than the isogenic wild-type whereas a strain blocked in the mutagenic pathway (rad6-1) is not mutable after the same treatment. Allele specificities were found. In particular the lys1-1 mutation is not reversible by formaldehyde. Higher concentrations of formaldehyde induce efficiently the cytoplasmic "petite" mutation in non-growing conditions when a lethal effect is noticeable. The growth phase as well as the physiological state influence this mutagenic effect. The mutagenic effect of formaldehyde in yeast is discussed in relation with the repair processes involved.