A highly conserved sequence is a novel gene involved in de novo vitamin B6 biosynthesis.
The Cercospora nicotianae SOR1 (singlet oxygen resistance) gene was identified previously as a gene involved in resistance of this fungus to singlet-oxygen-generating phototoxins. Although homologues to SOR1 occur in organisms in four kingdoms and encode one of the most highly conserved proteins yet identified, the precise function of this protein has, until now, remained unknown. We show that SOR1 is essential in pyridoxine (vitamin B6) synthesis in C. nicotianae and Aspergillus flavus, although it shows no homology to previously identified pyridoxine synthesis genes identified in Escherichia coli. Sequence database analysis demonstrated that organisms encode either SOR1 or E. coli pyridoxine biosynthesis genes, but not both, suggesting that there are two divergent pathways for de novo pyridoxine biosynthesis in nature. Pathway divergence appears to have occurred during the evolution of the eubacteria. We also present data showing that pyridoxine quenches singlet oxygen at a rate comparable to that of vitamins C and E, two of the most highly efficient biological antioxidants, suggesting a previously unknown role for pyridoxine in active oxygen resistance.
Ehrenshaft
M
M
Department of Plant Pathology, North Carolina State University, Raleigh, NC 27695, USA. me1@unity.ncsu.edu
Bilski
P
P
Li
M Y
MY
Chignell
C F
CF
Daub
M E
ME
D000818:Animals; D001105:Archaea / Q000235:genetics; D001203:Ascomycota / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D001231:Aspergillus flavus / Q000235:genetics / Q000378:metabolism; D001419:Bacteria / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D005075:Biological Evolution; D017173:Caenorhabditis elegans / Q000235:genetics; D017124:Conserved Sequence; D019992:Databases as Topic; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D005656:Fungal Proteins / Q000235:genetics*; D008025:Ligases; D010088:Oxidoreductases; D010100:Oxygen; D011736:Pyridoxine / Q000096:biosynthesis / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D026082:Singlet Oxygen; D014169:Transformation, Bacterial
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D005656:Fungal Proteins; C113268:PDX1 protein, Cercospora nicotianae; C098854:PdxJ protein, E coli; C060787:pdxA protein, E coli; D026082:Singlet Oxygen; D010088:Oxidoreductases; D008025:Ligases; D011736:Pyridoxine; D010100:Oxygen