A highly conserved sequence is a novel gene involved in de novo vitamin B6 biosynthesis

  • LI P
  • Chignell C
 et al. 
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The Cercospora nicotianae SOR1 (singlet ox- ygen 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


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  • P B I M Y LI

  • C F Chignell

  • M E Daub

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