Yeast cytochrome c-specific protein-lysine methyltransferase: coordinate regulation with cytochrome c and activities in cyc mutants.

The cytochromes c of fungi and higher plants contain one or two residues of epsilon-N-trimethyllysine, whose biological role is unknown. A cytochrome c-specific S-adenosylmethionine:protein-sysine methyltransferase (methylase) activity was shown to be present in extracts of the bakers' yeast Saccharomyces cerevisiae, and basic kinetic properties of this enzyme are described. The specific activity of the methylase was lower in extracts of cells grown under conditions of catabolite (glucose) repression or anaerobiosis where cytochrome c levels were low, compared with cells grown under derepressed conditions where cytochrome c levels were high. During anaerobic-to-aerobic adaptation, the methylase was induced in parallel with cytochrome c, thus suggesting that the syntheses of cytochrome c and cytochrome c methylase are coordinately regulated. None of the cyc strains surveyed (cyc1, cyc2, cyc3, cyc4, cyc5, and cyc6) had diminished levels of methylase, although some of them were completely or almost completely deficient in cytochrome c.