The cell-cycle-co-ordinated initiation of chromosomal replication is highly regulated. The ordered assembly and conformational change of specific proteins at the replication origin are crucial to the process of replication initiation. In Escherichia coli, ATP-DnaA molecules form multimeric complexes with the chromosomal origin of replication (oriC), and unwind the duplex DNA within oriC, resulting in initiation of replication. DnaA is a common protein in bacterial species and plays a main and crucial role in the initiation of chromosomal replication. Unlike well-characterized AAA+ (ATPase associated with various cellular activities) proteins such as chaperons and proteases, DnaA molecules stably take on a monomeric form and form homomultimers in a manner dependent on binding to oriC. The oriC region carries several DnaA-binding sites with various affinities. Recent progress in the analysis of DnaA and related proteins has revealed specific roles for the AAA+ unique motifs of DnaA. These results suggest mechanisms for recognition of ATP bound to DnaA, the co-operative binding of ATP-DnaA molecules on oriC, the formation of an ATP-DnaA-specific oriC complex, an initiation complex and regulatory hydrolysis of DnaA-bound ATP.
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