Manganese mutagenesis in yeast

Summary A medium was found in which manganese efficiently induces erythromycin-resistant mitochondrial mutations, and which is suitable for measuring Mn²⁺ uptake and the labelling of DNA (Fig. 1). Mn²⁺ uptake is stimulated by glucose and slowed down by cycloheximide (Fig. 2). Mg²⁺ competes with Mn²⁺ uptake much stronger than does Zn²⁺ (Fig. 3). All of the conditions which favour Mn²⁺ uptake also favour induction of erythromycin-resistant mutations (Tables 3, 4).Mn²⁺ strongly inhibits protein synthesis (Table 1). Nuclear DNA replication is also strongly inhibited by this cation, while mitochondrial DNA replication is only weakly inhibited during the first 3 h of labelling, but there is small if any increase of the label incorporation between the 3rd and 6th h of labelling (Table 2). The relation between label incorporation into mitDNA and mutation induction by manganese is not straightforward (Table 5).From among 11 divalent cations tested, only Mn²⁺ was capable of inducing mitochondrial erythromycin-resistant mutations (Table 6).