Single base substitution in an intron of oxidase gene compensates splicing defects of the cytochrome b gene

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Abstract
An extragenic suppressor mutation, mim2-1, which compensates yeast [Saccharomyces cerevisiae] mitochondrial mutants deficient in splicing of the cytochrome b gene was mapped and sequenced. The mutation was due to a single G .fwdarw. A transition in the long open reading frame of the 4th intron of the oxidase subunit 1 gene. It causes the replacement of a glutamic codon by a lysine codon and the expression of a novel mRNA maturase active in splicing. Evolution and regulatory connections between homologous introns of nonhomologous genes are discussed.