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DnaC

dnaC is a prokaryotic loading factor found in Escherichia coli that complexes with the C-terminus of helicase dnaB during the initial stages of prokaryotic DNA replication, loading dnaB onto DNA and inhibiting it from unwinding double stranded DNA (dsDNA) at a replication fork. Both dnaB and dnaC associate near the dnaA bound origin for each of the single stranded DNA molecules (ssDNA). Since DNA is antiparallel, one dnaB-dnaC complex is oriented in the opposite direction to the other dnaB-dnaC complex. After the assembly of dnaG, a primase, onto the N-terminus of dnaB, dnaC is released and dnaB will be allowed to begin unwinding dsDNA to make room for DNA polymerase to begin synthesizing the daughter strands.

dnaC Function
Association of dnaB-dnaC complex Since dnaC functions as a helicase loader, dnaB helicase is needed. Specifically, for dnaC function a complex with dnaB is formed. dnaB is a hexameric protein with helicase properties that allow it to unwind DNA at the origin site, oriC. When dnaC associates with dnaB and ATP, dnaB and dnaC form dimers with six dnaC polypeptides. These dimers a specific structure, containing a small lobe and a large lobe. The small lobe attaches to one monomer of the dnaB, while the large lobe associates with subunits of neighboring dnaB. When this happens, there is also a conformational change of the RecA fold on dnaB and the AAA+ domain of dnaC. The RecA fold is responsible for DNA binding and the AAA+ domain of dnaC is needed for ATP binding and hydrolysis. The new dnaB-dnaC complex formed can now aid in loading dnaB to the origin of replication. These interactions with the replication fork are impacted by the AAA+ domain on the C-terminal domain of dnaC. ATP is hydrolyzed to ADP and the complex is able to bind and close its ring-like structure around the DNA strand. When the dnaB-dnaC complex initially binds to the DNA, it is inactive. This reaction is the same one used to bind the complex to the ssDNA at the replication fork. In addition, interactions with dnaG on the N-terminal domain of dnaB are necessary to disrupt the dnaB-dnaC complex. This interaction and hydrolysis reaction releases dnaC from the C-terminal domain of dnaB. Once dnaC dissociates from the complex, dnaB is able to perform helicase activities for DNA replication. These allow for the ssDNA to be available to primase and other proteins necessary to create a complementary strand of the template DNA. == Current Research ==
Current Research
Current research is ongoing regarding dnaC and its role in prokaryotic DNA replication. Research groups are using a variety of physical and molecular methods to further knowledge. Topics include the role of single stranded binding proteins, potentially exploiting the dnaC-dnaB complex for peptide antibiotics, interactions with other proteins like dnaE, and others. Additionally, other prokaryotic helicase loaders, like DciA in bacteria, are being investigated due to their similar properties to dnaC. == References ==
Source: Wikipedia ↗
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