DnaA is a protein that activates initiation of DNA replication in prokaryotes. It is a replication initiation factor which promotes the unwinding of DNA at oriC. The onset of the initiation phase of DNA replication is determined by the concentration of DnaA. DnaA accumulates during growth and then triggers the initiation of replication. Replication begins with active DnaA binding to 9-mer (9-bp) repeats upstream of the oriC. Binding of DnaA leads to strand separation at the 13-mer repeats. This binding causes the DNA to loop in preparation for melting open by the helicase DnaB.
Read more about DnaA: Function