Mutations that alter the allosteric nature of cAMP receptor protein of Escherichia coli.

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Abstract
Mutations which permit cAMP binding protein (CRP) to act in the absence of cAMP have been isolated by in vitro mutagenesis of a plasmid containing the cloned crp gene. Adenylate cyclase deficient cells harbouring the mutant (crp*) plasmids exhibited a variety of fermentation profiles on MacConkey indicator plates containing various sugars. beta‐galactosidase synthesis in cells carrying the crp* plasmids was activated most by the addition of cGMP as well as cAMP. The sites of mutations which are responsible for the cAMP independent phenotype were determined by in vitro recombination and DNA sequencing. The amino acid substitutions in the mutant proteins were found in two specific regions of the crp gene encoding residues 53‐62 and 141‐148 of CRP polypeptide. The first region may participate in cAMP binding, while the second appears to be the inter‐domain region of the N‐terminal cAMP‐binding and C‐terminal DNA‐binding domains.