Abstract
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 beta-galactosidase production in strains which carry a lacZ gene altered such that it is transcribed from biotin operon promoters. Depression of beta-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.
Highlights
Introduction of thepBAllplasmid did not resultin greatly this prediction, I blocked expression of the 1.3 S geneby repression of its tuc promoter through introduction of the lacP allele on an F’ episome
Because the amount of biotin incorporated into the 1.3 S protein was >7-fold greater than that incorporated into BCCP, strains carrying the ptucl.3t plasmid had lower free biotin concentrations than strains lacking the plasmid
A trivial explanation for this effect would be the lowering of free biotin pools through covalent attachment of the biotin to the 1.3 S protein
Summary
I grown in the presence of 41 mM biotin plus 2 mM isopropyl thiogalactoside (to inactivatethe lacl repressor), these strains contained 46 units of @-galactosidase,about one-third of the maximally derepressed level. Because the amount of biotin incorporated into the 1.3 S protein was >7-fold greater than that incorporated into BCCP, strains carrying the ptucl.3t plasmid had lower free biotin concentrations than strains lacking the plasmid. Increased levels of protein biotination or in depletion of free biotin levels (Table 111), and the increased repression can be attributed to threepressor activity of the overproduced BirA protein rather than to its ligase activity. It should be lacZ)501 strain carrying the ptucl.3t plasmid gave only 4.2 noted that the overproduction of biotinated protein in the units of @-galactosidasewhen grown on 41 nM biotin.
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