Cloning and sequencing of a previously unidentified gene that is involved in the biosynthesis of heme in Escherichia coli.
We have isolated a number of porphyrin (Por)-synthesis mutants as light-resistant revertants of a light-sensitive strain delta visA (hemH) of Escherichia coli that accumulates protoPor IX in the cell. Among such mutants, we found a double mutant (H103) with mutations in hemA and in a new gene downstream of hemA. This new gene, designated hemK, was located at 27 min on the linkage map of the E. coli chromosome. By nucleotide (nt) sequencing, it was demonstrated that hemK forms part of the hemA-prfA-hemK operon and encodes 225 amino acids that show no significant homology to any protein in the standard databases. The mutant strain H103 formed small colonies and showed no catalase activity even in the presence of 5-aminolevulinic acid (ALA), indicating its inability to catalyze a step in the biosynthesis of heme from ALA. An extract of H103 cells has readily detectable ALA dehydratase and porphobilinogen deaminase activities. H103 cells carrying a plasmid that included only hemA as an insert accumulated protoPor and coproPor, but showed no sensitivity to light, a result that suggests that it may be deficient in protoporphyrinogen oxidase activity.
Nakayashiki
T
T
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Nishimura
K
K
Inokuchi
H
H
D000445:Aldehyde Oxidoreductases / Q000235:genetics; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D002374:Catalase / Q000032:analysis; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D006418:Heme / Q000096:biosynthesis*; D011163:Hydroxymethylbilane Synthase / Q000032:analysis; D008027:Light; D008969:Molecular Sequence Data; D009876:Operon; D000623:Porphobilinogen Synthase / Q000032:analysis; D011496:Protein Methyltransferases; D011836:Radiation Tolerance / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D006418:Heme; D002374:Catalase; D000445:Aldehyde Oxidoreductases; C067282:glutamyl tRNA reductase; D011496:Protein Methyltransferases; C092404:prmC protein, E coli; D011163:Hydroxymethylbilane Synthase; D000623:Porphobilinogen Synthase