Sterol synthesis and viability of<i>erg11</i> (cytochrome P450 lanosterol demethylase) mutations in<i>Saccharomyces cerevisiae</i> and<i>Candida albicans</i>

<jats:title>Abstract</jats:title><jats:p>The identification of the precise structural features of yeast sterol molecules required for the essential “sparking” function has been a controversial area of research. Recent cloning and gene disruption studies in<jats:italic>Saccharomyces cerevisiae</jats:italic> have shown that C‐24 methylation (<jats:italic>ERG6</jats:italic>), C‐5 desaturation (<jats:italic>ERG3</jats:italic>) and Δ<jats:sup>8</jats:sup>‐Δ<jats:sup>7</jats:sup> isomerization (<jats:italic>ERG2</jats:italic>) are not required, while C‐14 demethylation (<jats:italic>ERG11</jats:italic>) and C‐14 reduction (<jats:italic>ERG24</jats:italic>) are each required for aerobic viability. Earlier observations had indicated that C‐14 demethylase deficient strains could be restored to aerobic growth by suppressor mutations that caused a deficiency in C‐5 desaturase. These strains were reported to synthesize some ergosterol, indicating that they contained leaky mutations in both<jats:italic>ERG11</jats:italic> and<jats:italic>ERG3</jats:italic>, thereby making it imposssible to determine whether the removal of the C‐14 methyl group was required for aerobic viability. The availability of the<jats:italic>ERG11</jats:italic> and<jats:italic>ERG3</jats:italic> genes has been used in this study to construct strains that contain null mutants in both<jats:italic>ERG11</jats:italic> and<jats:italic>ERG3</jats:italic>. Results show that these double disruption strains are viable and that spontaneously arising suppressors of the<jats:italic>ERG11</jats:italic> disruption are<jats:italic>erg3</jats:italic> mutants. The<jats:italic>erg11</jats:italic> mutants of<jats:italic>S. cerevisiae</jats:italic> are compared to similar mutants of<jats:italic>Candida albicans</jats:italic> that are viable in the absence of the<jats:italic>erg3</jats:italic> lesion.</jats:p>