Disease relevance of HEM13

• Taken together, these results suggest that induction of HEM13 occurs in part through relief of repression exerted by Rox1p and Cyp1p, and in part by activation mediated partly by Cyp1p under heme-deficiency and by unknown factors under oxygen-deficiency [1].
• Here we report the cloning of the hemF gene, encoding the aerobic coproporphyrinogen III oxidase from Escherichia coli, by functional complementation of a Saccharomyces cerevisiae HEM13 mutant [2].
• Hereditary coproporphyria (HCP), an autosomal dominant acute hepatic porphyria, results from mutations in the gene that encodes coproporphyrinogen III oxidase (CPO) [3].
• We studied SHY1, the yeast homologue of SURF1, with an aim to obtain a better understanding of the molecular pathogenesis of cytochrome c oxidase (COX) deficiency in SURF1 mutant cells from Leigh syndrome patients [4].
• Some nutritional factors affecting the production of cholesterol oxidase (COX) by Rhodococcus equi no [5].

High impact information on HEM13

• HAP1 and ROX1 form a regulatory pathway in the repression of HEM13 transcription in Saccharomyces cerevisiae [6].
• Mutants containing wild type apocytochrome c in mitochondria lack COX, suggesting that only the folded and mature protein is able to promote COX assembly [7].
• Cytochrome c oxidase (COX), the terminal enzyme of the mitochondrial respiratory chain, catalyzes the transfer of electrons from reduced cytochrome c to molecular oxygen [7].
• Effects of anoxia and the mitochondrion on expression of aerobic nuclear COX genes in yeast: evidence for a signaling pathway from the mitochondrial genome to the nucleus [8].
• HEM13 UAS conferred a 2-4-fold oxygen/heme control on a heterologous reporter gene [9].

Biological context of HEM13

• A series of deletions in the HEM13 promoter identified at least four regulatory regions that are required for HEM13 regulation [1].
• To investigate further the function of CYP1, we analysed its effects on the transcription of two genes, HEM13 and 14DM, which are preferentially expressed in anaerobiosis [10].
• HEM13 UAS is composed of two subelements: a 16-base pair sequence binding a constitutive factor acting as a transcriptional activator, and a 5'-flanking 20-base pair GC-rich region [9].
• We have isolated the HEM13 gene by functional complementation of a hem13 gene by functional complementation of a hem13 mutant and determined its nucleotide sequence [11].
• The predicted amino acid sequence of the HemF protein is 44% identical to that of the coproporphyrinogen oxidase encoded by the yeast HEM13 gene [12].

Anatomical context of HEM13

• To investigate the interaction of the presequence of the precursor of yeast cytochrome C oxidase subunit IV (COX IV) with phospholipid membranes, a series of single- and double-cysteine-substituted peptide variants derived from the 25-residue NH2-terminal presequence has been synthesized and modified with nitroxide spin labels [13].

Associations of HEM13 with chemical compounds

• HEM13 encodes coproporphyrinogen oxidase which catalyses the sixth enzymatic step in the heme biosynthetic pathway and 14DM encodes lanosterol-14-demethylase which is involved in sterol biosynthesis and is a member of the cytochrome P450 family [10].
• The absence of heme, the end product, led to an important increase of coproporphyrinogen III oxidase activity, while the activity of 5-aminolevulinate synthase, the first enzyme of the pathway, was not changed [14].
• This phase is completely quenched upon inclusion of 100 microM ferricyanide in the medium and originates from a second order reaction of COX with the excess Ru-102-Cyt c2+ generated by the flash in a solution [15].
• Assembly of COX was analysed in a shy1 null mutant strain by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) [4].
• In addition, NH4Cl, NaCl and Tween 80 also exhibited enhancing effects on COX production, being maximal at 0.1% (w/v), 0.2% (w/v) and 1.0% (v/v) respectively [5].

Regulatory relationships of HEM13

• In the absence of heme, Cyp1p activated HEM13 and strongly repressed ROX1, allowing de-repression of HEM13 [1].
• The results show that in anaerobic and in heme-deficient cells, CYP1 activates the transcription of HEM13 and inhibits that of 14DM [10].
• Cell extracts of a hem4 mutant incubated with delta-aminolevulinate accumulated coproporphyrin III suggesting a block in coproporphyrinogenase, the enzyme which converts coproporphyrinogen III to protoporphyrinogen [16].

Other interactions of HEM13

• Furthermore, oxygen repression of the hypoxic HEM13 gene was not affected by the deletion nor was this putative ROX1 gene regulated positively by oxygen as is the case for the S. cerevisiae gene [17].
• The transcriptional activator HAP1 is demonstrated to be required for the full-level expression of HEM13 in the absence of heme [6].
• We addressed the requirements for Tup1-Ssn6 recruitment to two hypoxic genes, ANB1 and HEM13, by using chromatin immunoprecipitation assays [18].
• Six of the seven mutants were blocked in a different enzyme activity: 5-aminolevulinate synthase, porphobilinogen synthase, uroporphyrinogen I synthase, uroporphyrinogen decarboxylase, coproporphyrinogen III oxidase and ferrochelatase [14].

Analytical, diagnostic and therapeutic context of HEM13

• This report describes an analysis of HEM13 UAS and of the Rox1p-responsive sites by electrophoretic mobility shift assays, DNase I footprinting, and mutational mapping [9].
• Two degenerate oligonucleotides corresponding to amino- and carboxyl-terminal protein segments were used in a polymerase chain reaction for the amplification of a major portion of subunit VII (residues 1-52), which was then used for the cloning of complete COX VII [19].
• COX VII exists as a single copy per haploid genome as shown by Southern blot and gene disruption [19].
• However, our observations, based on 2D-PAGE analysis of mitochondria labelled in vitro, now provide the first direct evidence that COX assembly is impaired in a Deltashy1 strain [4].

References