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 mu M-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-competiti
ve in nature with an inhibition constant (K-i) of about 8.25 mu M. 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 n
ot degraded. The Delta cya mutants of E. coil are unable to continue DNA sy
nthesis in the absence of de novo protein synthesis and the initiation of D
NA replication in these mutants takes place from oriC. (C) 1999 Societe fra
ncaise de biochimie et biologie moleculaire/Editions scientifiques et medic
ales Elsevier SAS.