Search results
Results from the WOW.Com Content Network
A helicase–primase complex (also helicase-primase, Hel/Prim, H-P or H/P) is a complex of enzymes including DNA helicase and DNA primase. A helicase-primase associated factor protein may also be present. [1] The complex is used by herpesviruses, in which it is responsible for lytic DNA virus replication.
The enzyme has both primase and polymerase functions in addition to helicase function. The gene coding for it is found in a prophage. [17] It bears homology to ORF904 of plasmid pRN1 from Sulfolobus islandicus, which has an AEP PrimPol domain. [23] Vaccinia virus D5 and HSV Primase are examples of AEP-helicase fusion as well. [12] [6]
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.
Helicase is an enzyme which breaks hydrogen bonds between the base pairs in the middle of the DNA duplex. Its doughnut like structure wraps around DNA and separates the strands ahead of DNA synthesis. In eukaryotes, the Mcm2-7 complex acts as a helicase, though which subunits are required for helicase activity is not entirely clear. [2]
T7 DNA helicase (gp4) is a hexameric motor protein encoded by T7 phages that uses energy from dTTP hydrolysis to process unidirectionally along single stranded DNA, separating the two strands as it progresses. It is also a primase, making short stretches of RNA that initiates DNA synthesis. [1] It forms a complex with T7 DNA polymerase.
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.
The primase and polymerase move in the opposite direction of the fork, so the enzymes must repeatedly stop and start again while the DNA helicase breaks the strands apart. Once the fragments are made, DNA ligase connects them into a single, continuous strand. [ 3 ]
DNA helicases are responsible for unwinding the double-stranded DNA during chromosome replication. Helicases in eukaryotic cells are remarkably complex. [106] The catalytic core of the helicase is composed of six minichromosome maintenance (Mcm2-7) proteins, forming a hexameric ring. Away from DNA, the Mcm2-7 proteins form a single ...