Abstract
The plasma-membrane-bound ferrireductase activity of ras1 and ras2 mutants of Saccharomyces cerevisiae is not induced in response to iron limitation. This phenotype was suppressed by the bcy1 mutation in ras2 but not in ras1 mutants. The cellular haem content of ras-1-bearing strains decreased dramatically when cells were grown in semi-synthetic medium (low yeast extract content), which could account for their very low ferrireductase activity. The ferrireductase activity of cdc25 and cdc35 mutants dropped when the cells were shifted to a non-permissive temperature. This drop was prevented in the double mutant cdc35 sra5 by adding cyclic AMP to the growth medium. We propose that ferrireductase activity is under the control of a cyclic AMP-dependent protein phosphorylation.