GENE INTERACTIONS BETWEEN POTASSIUM-SENSITIVE AND POTASSIUM-RESISTANT MUTATIONS OF PARAMECIUM TETRAURELIA

Two unlinked recessive mutations (ks-1 and ks-2 ) have been induced in Paramecium tetraurelia stock 51. Wild-type survives and grows when up to 30 mm KCl is added to the medium, but the mutants cease to grow and die when added KCl reaches 20-25 m m. These K(+)-sensitives have been crossed to stocks containing the K(+)-resistant genes, fA (very resistant) and kA (moderately resistant). All four genes are unlinked. Double mutants of ks-1 and either kA or fA are as resistant as the resistant member of the pair. Doubles of ks-2 and kA are like wild type, and doubles of ks-2 and fA are shifted from high resistance toward wild type. Gene ks-2 acts like a suppressor of kA and fA. This suppression can be understood in terms of the known biochemical defects of the mutants.