CLONING AND CHARACTERIZATION OF THE BACILLUS-SUBTILIS BIRA GENE ENCODING A REPRESSOR OF THE BIOTIN OPERON

The Bacillus subtilis birA gene, which regulates biotin biosynthesis, has been cloned and characterized. The birA gene maps at 202 degrees o n the B. subtilis chromosome and encodes a 36,200-Da protein that is 2 7% identical to Escherichia coli BirA protein. Three independent mutat ions in birA that lead to deregulation of biotin synthesis alter singl e amino acids in the amino-terminal end of the protein. The amino-term inal region that is affected by these three birA mutations shows seque nce similarity to the helix-turn helix DNA binding motif previously id entified in B. coli BirA protein. B. subtilis BirA protein also posses ses biotin-protein ligase activity, as judged by its ability to comple ment a conditional lethal birA mutant of E. coli.