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DNA polymerase alpha also known as Pol α is an enzyme complex found in eukaryotes that is involved in initiation of DNA replication. The DNA polymerase alpha complex consists of 4 subunits: POLA1 , POLA2 , PRIM1 , and PRIM2 .
DNA polymerase's ability to slide along the DNA template allows increased processivity. There is a dramatic increase in processivity at the replication fork. This increase is facilitated by the DNA polymerase's association with proteins known as the sliding DNA clamp. The clamps are multiple protein subunits associated in the shape of a ring.
The subunits of this complex are encoded by the ORC1, ORC2, ORC3, ORC4, ORC5 and ORC6 genes. [1] [2] [3] ORC is a central component for eukaryotic DNA replication, and remains bound to chromatin at replication origins throughout the cell cycle. [4] ORC directs DNA replication throughout the genome and is required for its initiation.
RNA Polymerases I, II, and III contain 14, 12, and 17 subunits, respectively. [8] All three eukaryotic polymerases have five core subunits that exhibit homology with the β, β’, α I, α II, and ω subunits of E. coli RNA polymerase. An identical ω-like subunit (RBP6) is used by all three eukaryotic polymerases, while the same α-like ...
[8] [14] Generally, the function and size of the ORC subunits are conserved throughout many eukaryotic genomes with the difference being their diverged DNA binding sites. The most widely studied origin recognition complex is that of Saccharomyces cerevisiae or yeast which is known to bind to the autonomously replicating sequence (ARS). [ 15 ]
DNA polymerase epsilon is a member of the DNA polymerase family of enzymes found in eukaryotes. It is composed of the following four subunits: POLE (central catalytic unit), POLE2 (subunit 2), POLE3 (subunit 3), and POLE4 (subunit 4).
The purified enzyme has typically 10–12 subunits (12 in humans and yeast) and is incapable of specific promoter recognition. [11] Many subunit-subunit interactions are known. [12] DNA-directed RNA polymerase II subunit RPB1 – an enzyme that in humans is encoded by the POLR2A gene and in yeast is encoded by RPO21. RPB1 is the largest subunit ...
The DNA clamp fold is found in bacteria, archaea, eukaryotes and some viruses. In bacteria, the sliding clamp is a homodimer composed of two identical beta subunits of DNA polymerase III and hence is referred to as the beta clamp. In archaea [5] and eukaryotes, it is a trimer composed of three molecules of PCNA.