BIOTIN SYNTHESIS IN HIGHER-PLANTS - ISOLATION OF A CDNA-ENCODING ARABIDOPSIS-THALIANA BIOB-GENE PRODUCT EQUIVALENT BY FUNCTIONAL COMPLEMENTATION OF A BIOTIN AUXOTROPH MUTANT BIOB105 OF ESCHERICHIA-COLI K12

Biotin synthase is involved in the conversion of dethiobiotin to bioti n in bacteria, yeast and higher plants. We isolated a complete cDNA (1 .3 kb) encoding A. thaliana bioB-gene product by functional complement ation of the bioB105 biotin auxotroph mutant of Escherichia coil K12 u sing an A. thaliana cDNA library. The open reading frame encodes a pre dicted protein of 378 amino acids and molecular mass of 41.634 Da. The bioB-gene product from A. thaliana shows specific regions of homology with the bioB-gene products off. coli, Serratia marcescens, Bacillus sphaericus, and Saccharomyces cerevisiae. The predicted amino acid seq uence of the plant protein contains the consensus region <GX(C)under b ar XED><(C)under bar XY><(C)under bar XQ> involved in the [2Fe-2S] clu ster binding. Furthermore, it does not present a transit peptide in it s N-terminal region suggesting that the A. thaliana bioB-gene product reported in this paper is located in the cytosolic compartment.