Second-site antibiotic resistance mutations in the ribosomal region of yeast mitochondrial DNA.

A large proportion of the spontaneous erythromycin resistant mutants isolated from a strain carrying a previously-induced chloramphenicol resistance mutation at cap3 do not map at ery1, the locus most often associated with mitochondrial erythromycin resistance. Most of the new mutations are also nonallelic at spil, spi2, and other known antibiotic resistance loci within the 21S rRNA gene; they are allelic with each other and define the new locus, ery2. Induced second-site erythromycin resistant mutants from the cap (r3) strain, as well as spontaneous or induced mutants from strains carrying a cap (r) 1 mutation, all tend to map at eryl. The cap (r3) mutation is apparently necessary for the expression of erythromycin resistance resulting from a second mutation at ery2.