Molecular and genetic characterization of a biotin biosynthetic gene in Arabidopsis encoding both 7,8-diaminopelargonic acid aminotransferase and dethiobiotin synthetase

Biotin is an essential enzyme cofactor required for different metabolic processes. Plants are a major source of biotin, however, the genes and the protein products of biotin biosynthetic pathway are not fully characterized. We have molecularly characterized the genetically defined Arabidopsis bio1 locus as encoding 7,8-diaminopelargonic acid (DAPA) aminotransferase. Molecular and genetic analysis revealed that the full length BIO1 cDNA is capable of producing a fusion protein that catalyzes not only DAPA aminotransferase, but also dethiobiotin synthetase (BIO3) which is another enzymatic step in the biotin biosynthetic pathway. We refer to this fusion-gene as BIO3/BIO1. This bifunctional enzyme was demonstrated by functional complementation of E. coli bioA - and bioD- mutants deficient in DAPA aminotransferase and dethiobiotin synthetase reactions, respectively. This gene organization is unique in biology and establishes that the BIO3/BIO1 gene has dual functions