Regulatory elements in the KlHEM1 promoter

In Kluyveromyces lactis the gene encoding 5-aminolevulinate synthase, KlHEM1, is regulated at the transcriptional level by carbon source and oxygen availability. The KlHEM1 promoter, fused to the reporter lacZ gene, has been analysed by deletion and direct mutagenesis techniques in order to find regulatory elements functionally relevant in this transcriptional regulation. Two regulatory regions which contain the consensuses for KlGcr1p and KlMig1p binding are functional in the promoter. Regulation by carbon source is oppositely dependent on KlGcr1p and KlMig1p, as also confirmed by the use of mutants in these regulatory factors. A pyrimidine-rich element is necessary for full expression of KlHEM1 both in aerobic and hypoxic conditions. Deletion analyses show that a regulatory sequence included in the region − 656 to − 558 is also necessary to reach high KlHEM1 expression in hypoxia. Hypoxic expression and repression caused in this condition by externally added deuteroporphyrin IX is independent of the consensuses for KlHap1p and KlBuf1p binding. Effects caused by disruption of the genes coding for the regulatory factors KlHap1p, KlRox1p and KlMot3p on KlHEM1 aerobic transcription do not fully explain the differences observed between normoxic and hypoxic expression.