1887

Abstract

The glycine-cleavage enzyme system ( and gene products) provides C units for cellular methylation reactions. Both the GcvA and leucine-responsive regulatory (lrp) proteins are required for regulation of the operon. One model proposed for regulation is that Lrp plays a structural role, bending the DNA to allow GcvA to function as either an activator or a repressor in response to environmental signals. This hypothesis was tested by replacing all but the upstream 22 bp of the Lrp-binding region in a fusion with the l1A site from phage λ. Integration host factor (IHF) binds the l1A site and bends the DNA about 140°. Shifting the l1A site by increments of 1 base around the DNA helix resulted in IHF-dependent activation and repression of expression that were face-of-the-helix dependent. Activation was also dependent on the GcvA protein, and repression was dependent on both the GcvA and GcvR proteins, demonstrating that the roles for these proteins were not altered. The results are consistent with Lrp playing primarily a structural role in regulation, although they do not completely rule out the possibility that Lrp also interacts with another -regulatory protein or with RNA polymerase.

Keyword(s): DNA bending , gcv operon , GcvA , IHF and Lrp
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/content/journal/micro/10.1099/13500872-145-3-569
1999-03-01
2019-10-23
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http://instance.metastore.ingenta.com/content/journal/micro/10.1099/13500872-145-3-569
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