Activation of the bgl operon by adaptive mutation |
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Authors: | Hall BG |
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Institution: | Biology Department, University of Rochester, New York 14627, USA. drbh@uhura.cc.rochester.edu |
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Abstract: | In growing Escherichia coli K12 cells, the cryptic bgl operon is activated
98% of the time by insertions of IS1 or IS5 into the control region,
designated bglR. The activated bgl operon permits utilization of the
beta-glucoside sugar arbutin as a sole carbon and energy source. The bgl
operon is also activated by late-occurring mutations during prolonged
selection on arbutin. The late-occurring mutations that occurred during
prolonged carbon starvation in the presence of arbutin were "adaptive
mutations" because they were specific to the presence of arbutin, and they
did not occur during prolonged starvation in the absence of arbutin. The
spectrum of late-arising mutations differed from that of early-arising,
growth-dependent mutations in that 20% of the late-arising mutants resulted
from mutations at the hns locus. This provides the first direct evidence
for adaptive mutagenesis mediated by the insertion of IS elements. Because
no special genetic background is required to select Bgl+ mutants, this
affords the opportunity to study IS-element-mediated adaptive mutagenesis
in a variety of genetic backgrounds, including the backgrounds of natural
isolates of E. coli.
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