Initiation of DNA replication in delta cya mutants of Escherichia coli K12.

The purified DnaA protein has a high affinity for cyclic AMP (cAMP). Using equilibrium dialysis, we determined the K(A) value for cAMP as 0.819 muM(-1). The number of cAMP binding sites per DnaA protein molecule was calculated to be 1.04. This binding was quite specific for cAMP. ATP was also bound by DnaA protein and inhibited cAMP binding. This inhibition was non-competitive in nature with an inhibition constant (K(i)) of about 8.25 muM. However, in vivo we have found not only that the DnaA protein level is reduced in a cyclase deletion mutant strain, Delta++ cya, but also that DnaA protein is not degraded. The Delta cya mutants of E. coli are unable to continue DNA synthesis in the absence of de novo protein synthesis and the initiation of DNA replication in these mutants takes place from oriC.