Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 103

Conversion to the DnaA-ADP state occurs primarily by two mechanisms following initiation of DNA replication. As mentioned above, only the ATP-bound form can bind all of the DnaA boxes in oriC. Only when all of the sites are bound can the structure form that will be needed to open the DUE to allow replication to initiate (Figure 1.15). This helps the DnaA protein to act as a switch that is largely independent of its concentration because other cellular inputs can control the ATP-bound versus ADP-bound state of DnaA. One cellular input that reduces the pool in the DnaA-ATP state involves the presence of the assembled replication fork at the origin region immediately after initiation of replication. The presence of the β sliding-clamp protein causes DnaA to hydrolyze ATP to ADP by interacting with another protein, a relative of DnaA called Hda (for homology to DnaA) (see Camara et al., Suggested Reading). This process is sometimes referred to as regulatory inactivation of DnaA, or RIDA. A second input that reduces the pool of DnaA-ATP involves a locus in the chromosome called datA. The datA locus, which is about 1 kb in length, has five DnaA-binding sites and a binding site for IHF. Binding of DnaA and IHF to this locus induces an endogenous ATPase activity of the DnaA protein, coaxing it into the inactive DnaA-ADP form in a process abbreviated as DDAH (datA-dependent DnaA-ATP hydrolysis). How specifically DDAH is controlled with the cell cycle remains unknown.