Mitochondrial and nuclear mitoribosomal suppressors that enable misreading of ochre codons in yeast mitochondria : II. Specificity and extent of suppressor action.

We describe studies on the action spectra of the mitochondrial suppressor mim3-1 and the three alleles of nuclear suppressor nam3. Their specificity of action was tested on 516 mit (-) mutations located in different mitochondrial genes. The degree of suppression was quantified by the extent of cytochrome oxidase and cytochrome b synthesis. We show that the four suppressors are allele-specific gene-nonspecific informational suppressors. They would act by changing the structure of the small mitoribosomal subunit which would decrease fidelity of translation enabling misreading of some but not all ochre codons. The implications of the results on the role of intron encoded maturases are discussed.