HAP1 and ROX1 form a regulatory pathway in the repression of HEM13 transcription in Saccharomyces cerevisiae.

Abstract

HEM13 of Saccharomyces cerevisiae encodes coproporphyrinogen oxidase, an enzyme in the heme biosynthetic pathway. Expression of HEM13 is repressed by oxygen and heme. This study investigated the regulatory pathway responsible for the regulation of HEM13 expression. The transcriptional activator HAP1 is demonstrated to be required for the full-level expression ofHEM13 in the absence of heme. It is also shown that the repression ofHEM13 transcription caused by heme involves the H4P] and ROXI gene products; a mutation in either gene results in derepression of HEM13 expression. The heme-dependent expression of ROXI was found to require functional HAP1, leading one to propose that repression of HEM13 results from a pathway involving HAPI-mediated regulation of ROXI transcription in response to heme levels followed by ROX1-mediated repression of HEM13 transcription. In support of this model, expression of ROXI under control of the GAL promoter was found to result in repression of HEM13 transcription in a hap] mutant strain. The ability of ROX1 encoded by the galactose-inducible ROXI construct to function in the absence of HAP1 indicates that the only role of HAP1 in repression of HEM13 is to activate ROXI transcription.

Dynamical Remodeling of the Transcriptome during Short-Term Anaerobiosis in Saccharomyces cerevisiae: Differential Response and Role of Msn2 and/or Msn4 and Other Factors in Galactose and Glucose Media

“…Here we observed the down-regulation of ROX1 and MOT3, whose expression is regulated by Hap1 and heme (17,47,74), and up-regulation of UPC2, whose expression is repressed by Rox1 (51). Interestingly, HAP1, which serves an essential function under anaerobiosis (13), was chronically up-regulated in both media.…”

The Rox1 repressor of the Saccharomyces cerevisiae hypoxic genes is a specific DNA-binding protein with a high-mobility-group motif.

“…Only the unlabelled hypoxic consensus sequence reduced the intensity of the gel retardation band formed by Roxl binding to the labelled consensus sequence; neither the excess dI-dC present in all binding reactions nor a nonhomologous synthetic DNA was capable of competing for Roxl binding. The hypoxic consensus sequence appears in the upstream region of all the genes repressed by Roxl and in a number of cases has been demonstrated to be within the region responsible for repression (7,14,20,36). The ANBl gene, which is very tightly repressed under aerobic conditions, has two operator sequences each of which contains two copies of the consensus sequence (20).…”

“…These genes encode functions that help the cell utilize limiting molecular oxygen under partially anaerobic conditions and include genes coding for enzymes that utilize molecular oxygen as an electron acceptor in the biosynthesis of heme (HEM13 [14,44,48,49]), sterol (ERG11 and CPR1 [43,44]), and fatty acids (OLE1 [24a, 38]), alternate cytochrome subunits (COXSb [1, la, 6, 7] and CYC7 [18,23]), an alternate mitochondrial ADP-ATP translocator (ACC3 [16,36]), and an alternate translation initiation factor (ANB1 [20-22, 25, 33).…”

Balanced globin protein expression and heme biosynthesis improve production of human hemoglobin in Saccharomyces cerevisiae

“…In 254 terms of bound heme level, H3 still stood out with almost 5 fold of pIYC04, followed by H3H2H12, 255 2.8 fold, and H12, 2.4 fold (Fig 2B). 256 257 HEM13 transcription is known to be negatively regulated by oxygen and heme (Zagorec and Labbe-258 Bois, 1986) through HAP1 and ROX1 (Keng, 1992). Overexpression of the genes in the heme 259 biosynthesis pathway (strains H2, H3, H12, H2H3, H2H12 and H3H2H12) resulted in certain 260 improvements on heme levels (Fig 2B) which might induce feedback inhibition on the synthesis of 261…”