Expression of the biotin biosynthetic operon of Escherichia coli is regulated by the rate of protein biotination

In Escherichia coli biotin biosynthesis is repressed by high concentrations of exogenous biotin. This paper reports that upon high level production of the apo form of a biotinated protein, biotin operon expression was derepressed by 8-10-fold. The biotinated protein studied was the 1.3 S subunit of Propionibacterium shermanii, and transcarboxylase derepression was assayed by β-galactosidase production in strains which carry a lacZ gene altered such that it is transcribed from biotin operon promoters. Depression of β-galactosidase synthesis upon production of the apo 1.3 S protein was observed over a several hundred-fold range of biotin concentrations and also resulted in an increased level of biotin operon expression at maximally repressing biotin concentrations. Biotin operon derepression by apobiotin protein production seems a direct consequence of the properties of the biotin repressor protein which also functions as the ligase catalyzing the covalent attachment of biotin to apoproteins.