Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 102

DnaA is essential for initiating DNA replication at oriC and along with other components also helps to regulate the timing of DNA replication. DnaA primarily affects the frequency of initiation by changes in the ATP-binding versus ADP-binding state of DnaA and by access of DnaA to oriC. DnaA must be in its ATP-bound state to form the structure used to separate the DNA strands at oriC to initiate DNA replication. DnaA hydrolyzes ATP slowly; therefore, other factors are required to stimulate its ATPase activity to inactivate it until it is needed for the next round of DNA replication. The affinity of DnaA for the various binding sites within oriC (see “Origin of Chromosomal Replication” above) allows a mechanism for the origin to be identified but not immediately used as an origin until all conditions are in place for replication. A number of processes control the pool of DnaA found in the ATP-bound state. Reducing the pool of DnaA-ATP following initiation is an important mechanism for delaying reinitiation, thereby allowing replication to proceed in an orderly fashion. The production of new DnaA also plays a role in the ratio of ATP-bound versus ADP-bound DnaA, and because of the high ATP concentration in cells, newly made DnaA will be bound by ATP.