What is the role of the DnaA protein in DNA replication?
DnaA is a protein that activates initiation of DNA replication in bacteria. It is a replication initiation factor which promotes the unwinding of DNA at 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.
Is DnaA a helicase?
DnaA and DnaC are specifically required at the stage of initiation of DNA replication from the E. coli replication origin (oriC) to load the replicative DNA helicase (DnaB) at this chromosomal site. DnaA is a protein that binds ATP and also DNA, but in a sequence-specific manner.
How is initiation of bacterial DNA replication controlled?
One regulatory pathway ensures that initiation of DNA replication from the chromosomal origin, oriC, is synchronous and occurs at the proper time in the bacterial cell cycle. A major player in this pathway is SeqA protein and involves its ability to bind preferentially to oriC when it is hemi-methylated.
Does DnaA require ATP?
coli Dnaa-Atp Is in Origin Recognition and Regulation of Initiation Timing. Although DnaA-ATP is required for activation of wild type E. coli oriC in vitro, it has been known for several decades that at least some of the DnaA in functional E. coli orisomes can be in the ADP-bound form (Yung et al., 1990).
What is 9mer and 13mer?
It contains repetitive 9-base pair and 13-base pair sequences (known as the ‘9-mer’ and ’13-mer’ regions). These sequences are AT rich regions, which melt at lower temperatures than DNA containing GC pairs. These regions are postulated to help melt the DNA duplex in the oriC region for initiation of DNA replication.
What are three ways bacteria regulate replication initiation to ensure it occurs at the right time?
Three key negative regulation mechanisms preventing reinitiation from the newly replicated origins have been described in E. coli : (1) inhibition of DnaA activity, (2) titration of the free form of DnaA, and (3) sequestration of the oriC .
How initiation of replication is regulated in prokaryotes?
Regulation. Chromosome replication in bacteria is regulated at the initiation stage. DnaA-ATP is hydrolyzed into the inactive DnaA-ADP by RIDA (Regulatory Inactivation of DnaA), and converted back to the active DnaA-ATP form by DARS (DnaA Reactivating Sequence, which is itself regulated by Fis and IHF).
What is the function of dnaC?
dnaC is a loading factor that complexes with the C-terminus of helicase dnaB and inhibits it from unwinding the dsDNA at a replication fork. A dnaB and dnaC associate near the dnaA bound origin for each of the ssDNA.
What are 9-mers and 13-mers?
The 9-mers and 13-mers are the repetitive sequences shown in Figure 12-5. Multiple copies of DnaA protein bind to the 9-mers at the origin and then “melt” (separate the strands of) the (more…) Binding of DnaA to the oriC 9-mers facilitates the initial strand separation, or “melting,” of E.