DnaA, assembly

The polymerase holoenzyme assembles. The DNA polymerase ITT holoen-zyme assembles on the prepriming complex, initiated by interactions between DnaB and the sliding clamp subunit of DNA polymerase 111. These interactions also trigger ATP hydrolysis within the DnaA subunits, signaling the initiation of DNA replication. The breakup of the DnaA assembly prevents additional rounds of replication from beginning at the replication origin. 

The assembly of the ORC is the first step in the preparation for replicalion. In human beings, the ORC is composed of six different proteins, each homologous to DnaA. These proteins likely come together to form a hexam-eric structure analogous to the assembly formed by DnaA. 

Replication begins when DnaA monomers bind to oriC forming a nucleosome-like structure. This requires ATP and HU. Localized melting permits the binding of the DnaB/DnaC complex. Dissociation of DnaC allows the DnaB helicase to unwind the helix in preparation for DNA replication. The DnaA complex dissociates, SSB keeps the single strands apart and the replication fork is now ready for the assembly of the replisome. 

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