Regulatory elements in the KIHEM1 promoter

摘要

In Kluyveromyces lactis the gene encoding 5-aminolevulinate synthase, KIHEM1, is regulated at the transcriptional level by carbon source and oxygen availability. The KIHEM1 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 KlGcrlp and KlMiglp binding are functional in the promoter. Regulation by carbon source is oppositely dependent on KlGcrlp and KlMiglp, as also confirmed by the use of mutants in these regulatory factors. A pyrimidine-rich element is necessary for full expression 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 KlHaplp and KlBuflp binding. Effects caused by disruption of the genes coding for the regulatory factors KlHaplp, KlRoxlp and KlMot3p on KlHEM1 aerobic transcription do not fully explain the differences observed between normoxic and hypoxic expression.