THE DAN1 GENE OF SACCHAROMYCES-CEREVISIAE IS REGULATED IN PARALLEL WITH THE HYPOXIC GENES, BUT BY A DIFFERENT MECHANISM

The DAN1 gene is expressed under anaerobic conditions in yeast and com pletely repressed during aerobic growth. The function of the gene is u nknown, and genetic disruption had no effect on fitness which could be detected, even upon prolonged anaerobic growth. Expression of DAN1 wa s constitutive in a heme-deficient strain, indicating that heme partic ipates in repression. Expression was blocked by heme in anaerobic medi um, suggesting that heme acts as a negative co-effector rather than th rough its metabolic functions, i.e., in the production of a co-effecto r. Expression of DAN1 was regulated in parallel with the hypoxic gene ANB1, showing identical kinetics of induction and dose response to hem e. However, unlike ANB1, DAN1 is not regulated by the repressor of the hypoxic regulon, ROX1, as shown by observation of normal aerobic repr ession of DAN1 in a strain carrying a deletion of ROX1. These results indicate the existence of a parallel regulatory system which produces an identical response to oxygen by a different mechanism than that con trolling the hypoxic regulon. (C) 1997 Elsevier Science B.V.