Porphyrin mutants of Saccharomyces cerevisiae: Correlated lesions in sterol and fatty acid biosynthesis

The $\text{ole2}$, $\text{3}$ and $\text{4}$ mutants of yeast require an unsaturated fatty acid and methionine for growth and do not synthesise ergosterol. They have very similar sterol compositions and all accumulate lanosterol. The mutants lack cytochrome pigments and have negligible respiratory activity. Porphyrin intermediates alleviate the lipid requirement of $\text{ole2}$ and $\text{ole3}$ and restore respiratory competence. It is concluded that the primary defects in these mutants are lesions in porphyrin biosynthesis.