ISOLATION AND CHARACTERIZATION OF PARAMECIUM MUTANTS DEFECTIVE IN THEIR RESPONSE TO MAGNESIUM

Four mutant strains of Paramecium tetraurelia with a reduced ability t o respond behaviorally to Mg2+ have been isolated. Voltage-clamp analy ses showed that their Mg2+ insensitivity is associated with a reduced Ca2+-dependent Mg2+ current. The four mutants, which have been dubbed ''eccentric,'' result from recessive mutations in two unlinked loci, x ntA and xntB. Further analysis of xntA(1) showed it to be unlinked to any of the behavioral mutants of P. tetraurelia described previously, but it is allelic to d4-521, a ''K+-resistant'' strain, and d4-596, a ''Ba2+-shy'' mutant. The varied pleiotropic effects of xntA(1), which include increased resistance to Ni2+ and Zn2+ poisoning, suggest that the locus encodes a central regulator of cell function in Paramecium.