Blocking, Bending, and Binding: Regulation of Initiation of Chromosome Replication During the Cell Cycle by Transcriptional Modulators That Interact With Origin DNA.

Genome duplication is a critical event in the reproduction cycle of every cell. Because all daughter cells must inherit a complete genome, chromosome replication is tightly regulated, with multiple mechanisms focused on controlling when chromosome replication begins during the cell cycle. In bacteria, chromosome duplication starts when nucleoprotein complexes, termed orisomes, unwind replication origin () DNA and recruit proteins needed to build new replication forks.

Changing Perspectives on the Role of DnaA-ATP in Orisome Function and Timing Regulation.

Bacteria, like all cells, must precisely duplicate their genomes before they divide. Regulation of this critical process focuses on forming a pre-replicative nucleoprotein complex, termed the orisome. Orisomes perform two essential mechanical tasks that configure the unique chromosomal replication origin, to start a new round of chromosome replication: (1) unwinding origin DNA and (2) assisting with loading of the replicative DNA helicase on exposed single strands.

Blocking the Trigger: Inhibition of the Initiation of Bacterial Chromosome Replication as an Antimicrobial Strategy.

All bacterial cells must duplicate their genomes prior to dividing into two identical daughter cells. Chromosome replication is triggered when a nucleoprotein complex, termed the orisome, assembles, unwinds the duplex DNA, and recruits the proteins required to establish new replication forks. Obviously, the initiation of chromosome replication is essential to bacterial reproduction, but this process is not inhibited by any of the currently-used antimicrobial agents.

Low Affinity DnaA-ATP Recognition Sites in Make Non-equivalent and Growth Rate-Dependent Contributions to the Regulated Timing of Chromosome Replication.

Although the mechanisms that precisely time initiation of chromosome replication in bacteria remain unclear, most clock models are based on accumulation of the active initiator protein, DnaA-ATP. During each cell division cycle, sufficient DnaA-ATP must become available to interact with a distinct set of low affinity recognition sites in the unique chromosomal replication origin, , and assemble the pre-replicative complex (orisome) that unwinds origin DNA and helps load the replicative helicase. The low affinity -DnaA-ATP interactions are required for the orisome's mechanical functions, and may also play a role in timing of new rounds of DNA synthesis.

Origin recognition is the predominant role for DnaA-ATP in initiation of chromosome replication.

In all cells, initiation of chromosome replication depends on the activity of AAA+ initiator proteins that form complexes with replication origin DNA. In bacteria, the conserved, adenosine triphosphate (ATP)-regulated initiator protein, DnaA, forms a complex with the origin, oriC, that mediates DNA strand separation and recruitment of replication machinery. Complex assembly and origin activation requires DnaA-ATP, which differs from DnaA-ADP in its ability to cooperatively bind specific low affinity sites and also to oligomerize into helical filaments.