NUCLEAR INHERITANCE OF A GENE AFFECTING MITOCHONDRIAL GENE-EXPRESSION

Due to a deficiency in mitochondrial protein synthesis, Chinese hamste r lung (CHL) cell mutant Gal(-) 32 does not grow in galactose or fruct ose. This report examines the nuclear or cytoplasmic inheritance of th is single, recessive mutation. in a control experiment, fusion of Gal( +)TG(S)TK(-) cells with Gal(-)32TG(R)TK(+) cells resulted in tetraploi d hybrids (as verified by karyotyping) that were selected in hypoxanth ine/aminopterin/thymidine medium. The majority (2/3) of the control hy brids grew in galactose as expected since Gal(+) is dominant over Gal( -). Fusion of Rhodamine 6-G treated Gal(+)TG(S)TK(-) cells with Gal(-) 32TG(R)TK(+) cells resulted in Rhodamine 6-G-tetraploid hybrids that w ere selected in hypoxanthine/aminopterin/thymidine medium. The majorit y (7/12) of the Rhodamine 6-G-hybrids grew in galactose as expected fo r a nuclearly encoded gene considering that Rhodamine 6-G interferes w ith transmission of mtDNA but not nuclear DNA. Therefore, these result s are compelling in their demonstration of the nuclear origin of the G al(-)32 mutation.