Disease relevance of HEM12

• Modified uroporphyrinogen decarboxylase activity in a yeast mutant which mimics porphyria cutanea tarda [1].
• The amino acid sequence shares 50% identity with human and rat uroporphyrinogen decarboxylase and shows 40% identity with the N-terminus of an open reading frame described in Synechococcus sp. We determined the sequence of two hem12 mutations which lead to a totally inactive enzyme [2].
• To understand its function in cyanobacteria, we carried out yeast two-hybrid screening to identify specific proteins interacting with HtpG, and found out, HemE, uroporphyrinogen decarboxylase [3].

High impact information on HEM12

• Uroporphyrinogen decarboxylase, an enzyme of the haem-biosynthetic pathway, catalyses the decarboxylation of uroporphyrinogen to coproporphyrinogen and is encoded by the HEM12 gene in the yeast Saccharomyces cerevisiae [4].
• Four different point mutations were identified in seven 'leaky' mutants with residual modified uroporphyrinogen decarboxylase activity; each of three mutations was found in two independently isolated mutants [4].
• The mutations sites studied are situated far apart within the HEM12 gene located on chromosome IV [5].
• In heterozygous hem12-1/HEM12 diploid cells, a 50% decrease in decarboxylase activity led to an increased accumulation of porphyrins as compared with the wild-type HEM12/HEM12 diploid, which points to the semi-dominant character of the hem12-1 mutation [5].
• Nine new hem12 haploid mutants of baker's yeast (Saccharomyces cerevisiae), totally or partially deficient in uroporphyrinogen decarboxylase activity, were subjected to both genetic and biochemical analysis [5].

Biological context of HEM12

• PAP1 was mapped in a contig of three known (DBF4, TPI and HEM12), but so far unlinked, genes on chromosome IV [6].
• Mutational analysis of the HEM12 leader sequence was also performed to determine the role of small open reading frames (uORFs) present upstream of the HEM12 ORF [7].
• In contrast, the sui2 suppressor encoding the a subunit of eIF2 does not affect the hem12 phenotype [7].
• Plasmids containing these mutations were able to complement a hem6 mutant strain [8].
• We suggest that this motif is a binding site for the Pop3/Rpp38 proteins and we discuss other structural features of the RNA subunit and possible relationships to the protein subunit repertoire [9].

Associations of HEM12 with chemical compounds

• The purified enzyme has a minimum molecular mass of 38 kDa by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and 46 kDa by gel filtration, suggesting that yeast uroporphyrinogen decarboxylase is a monomer [10].
• 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 [11].
• A conserved cysteine residue in yeast uroporphyrinogen decarboxylase is not essential for enzymatic activity [8].
• Such approaches in this laboratory with protoporphyrinogen oxidase, coproporphyrinogen oxidase, and uroporphyrinogen decarboxylase have resulted in the production and purification of enzymes whose kinetic and physical parameters are essentially identical to those of proteins lacking the His6 tag [12].

Other interactions of HEM12

• The effect of the hem12 mutation is also partially reversed by the known SUI3 suppressor encoding the beta subunit of eIF2 [7].

Analytical, diagnostic and therapeutic context of HEM12

• Identification of amino acid changes affecting yeast uroporphyrinogen decarboxylase activity by sequence analysis of hem12 mutant alleles [4].
• Complementation tests with biochemically defined, haem-less strains showed that in seven mutants uroporphyrinogen decarboxylase was affected and that in three mutants the defect concerned ferrochelatase [13].

References