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DnaB helicase is an enzyme in bacteria which opens the replication fork during DNA replication.Although the mechanism by which DnaB both couples ATP hydrolysis to translocation along DNA and denatures the duplex is unknown, a change in the quaternary structure of the protein involving dimerisation of the N-terminal domain has been observed and may occur during the enzymatic cycle. [1]
Helicases move incrementally along one nucleic acid strand of the duplex with a directionality and processivity specific to each particular enzyme. Helicases adopt different structures and oligomerization states. Whereas DnaB-like helicases unwind DNA as ring-shaped hexamers, other enzymes have been shown to be active as monomers or dimers.
DnaC helps the helicase to bind to and to properly accommodate the ssDNA at the 13 bp region; this is accomplished by ATP hydrolysis, after which DnaC is released. Single-strand binding proteins (SSBs) stabilize the single DNA strands in order to maintain the replication bubble. DnaB is a 5'→3' helicase, so it travels on the lagging strand.
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. [1] A dnaB and dnaC associate near the dnaA bound origin for each of the ssDNA. [1] One dnaB-dnaC complex is oriented in the opposite direction to the other dnaB-dnaC complex due to the antiparallel nature ...
In prokaryotes, DnaA hydrolyzes ATP in order to unwind DNA at the oriC. This denatured region is accessible to the DnaB helicase and DnaC helicase loader. Single-strand binding proteins stabilize the newly formed replication bubble and interact with the DnaG primase. DnaG recruits the replicative DNA polymerase III, and replication begins.
The DnaC helicase loader then interacts with the DnaA bound to the single-stranded DNA to recruit the DnaB helicase, [9] which will continue to unwind the DNA as the DnaG primase lays down an RNA primer and DNA Polymerase III holoenzyme begins elongation. [10]
The primosome consists of seven proteins: DnaG primase, DnaB helicase, DnaC helicase assistant, DnaT, PriA, Pri B, and PriC. At each replication fork, the primosome is utilized once on the leading strand of DNA and repeatedly, initiating each Okazaki fragment, on the lagging DNA strand. Initially the complex formed by PriA, PriB, and PriC binds ...
This helicase translocates in the same direction as the DNA polymerase (3' to 5' with respect to the template strand). In prokaryotic organisms, the helicases are better identified and include dnaB, which moves 5' to 3' on the strand opposite the DNA polymerase.