Affiliation:
1. Department of Biological Sciences, Stanford University, Stanford, California 94305
Abstract
A strain of
Escherichia coli
in which the
lacZ
gene was fused to the
bioA
promoter was constructed. Colonies of this strain formed Lac
+
colonies on low-biotin agar (1.6 to 4.1 nM) and Lac
−
colonies on high-biotin agar (41 nM). This
lac-bio
fusion strain was used to study the question of whether cells growing on the biotin vitamers
d
-biotin-
d
-sulfoxide (BDS) and dethiobiotin (DTB) generate enough biotin to give maximal repression of β-galactosidase synthesis. Repression by high concentrations (400 nM) of BDS was almost maximal (about 96%), whereas DTB repression reached a saturation level of about 80% with increasing DTB concentrations. The levels of repression obtained with both vitamers were sufficient to cause the colonies to appear Lac
−
. When the
lac-bio
fusion was transduced into lines carrying mutations (
bis
) that prevent reduction of BDS to biotin, the transductants were not repressed by added BDS. Repression by BDS is unlikely to result from accumulation of extracellular biotin-related substances because (i) washed
bis
+
cells were not detectably derepressed when transferred into medium containing BDS and (ii) washed
bis
cells were not detectably repressed when transferred into medium in which
bis
+
cells had grown. Lactose agar plates containing high concentrations of DTB or BDS comprise an efficient selective medium for
bioB
or
bis
mutants and were used to isolate spontaneous mutations of these genes. This method should be adaptable to the selection of mutations in any biosynthetic pathway subject to end-product repression.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
15 articles.
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