A highly conserved sequence is a novel gene involved inde novovitamin B6 biosynthesis

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Abstract
TheCercospora 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 toSOR1occur 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 thatSOR1is essential in pyridoxine (vitamin B6) synthesis inC. nicotianaeandAspergillus flavus,although it shows no homology to previously identified pyridoxine synthesis genes identified inEscherichia coli. Sequence database analysis demonstrated that organisms encode eitherSOR1orE. colipyridoxine biosynthesis genes, but not both, suggesting that there are two divergent pathways forde novopyridoxine 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.

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