Involvement of cyclic AMP and its receptor protein in the sensitivity of Escherichia coli K 12 toward serine

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Abstract
A relationship between serine-induced growth sensitivity and the cAMP-CAP complex is established. Mutants of Escherichia coli K 12 deficient either in the cya or crp gene function exhibit a resistant phenotype on serine media although they harbor a relA allele normally leading to sensitivity toward serine. The presence of a crp * allele in a cya Δ rela background restores the sensitivity phenotype, while the analysis of serine resistant mutants selected from a crp * cya Δ relA strains shows that the mutation leading to resistance is located at, or very near, the crp gene, giving a more or less Crp- phenotype. In addition crp * cya Δ relA strains excrete large quantities of 2-ketobutyrate when grown on glucose M63 medium. This excretion is unambiguously linked to the presence of the crp * allele and is correlated with an enhanced threonine deaminase activity. Besides, the complex regulation exerted on the acetolactate synthase activities is discussed.