DnaA

DnaA is a replication initiation factor which promotes the unwinding or denaturation of DNA at oriC (around 240bp in Escherichia coli), during DNA replication in prokaryotes.

The oriC/DnaA complex formation and DNA unwinding requires ATP hydrolysis**.

The oriC site in E. coli has three AT rich 13mer regions (DUE's elements) followed by four 9mer regions. Around 10 dnaA molecules bind to the 9mer regions, which wrap around the proteins causing the DNA at the 13mer region to unwind. The denatured 13mer allows the recruitment of DnaB (helicase) complex with DnaC (helicase loader). DnaC helps the helicase to bind and accommodate properly to the ssDNA at the 13mer region, this is accomplished thanks to ATP hydrolysis after which DnaC is released. Single-strand-binding proteins (SSBs) help in keeping the double-helix from reforming at the replication bubble. The DnaB is a 5'->3' helicase, so it travels on the lagging strand. It associates with DnaG (a primase) to form the only primer for the leading strand and to add RNA primers on the lagging strand. The interaction between DnaG and DnaB is necessary to control the longitude of Okazaki fragments on the lagging strand. DNA polymerase III is then able to start DNA replication.