Sequencing analysis of mutation points in the biotin operon of biotin-overproducing Escherichia coli mutants

We analyzed mutation points of the biotin operon from biotin-overproducing mutants of Escherichia coli resistant to two biotin analogs, actithiazic acid and 5-(2-thienyl)-valeric acid, by DNA sequencing. The biotin operons cloned from these mutants were classified into three groups. One point mutation, which was a GC-->AT change within the operator overlapping the -10 region of the rightward (bioB) promoter, was considered to result in disruption of operator structure and enhancement of promoter activity. Two other point mutations, which were both GC-->AT changes just before and after the initiation codon of the bioB gene, were considered to activate the translation efficiency. These mutations significantly accelerated the biotin-forming activity from dethiobiotin in cell-free extracts.