Polymerase

A polymerase is an enzyme (EC 2.7.7.6/7/19/48/49) that synthesizes long chains of polymers or nucleic acids. DNA polymerase and RNA polymerase are used to assemble DNA and RNA molecules, respectively, by copying a DNA template strand using base-pairing interactions or RNA by half ladder replication. A DNA polymerase from the thermophilic bacterium, Thermus aquaticus (Taq) (PDB 1BGX, EC 2.7.7.7) is used in the polymerase chain reaction, an important technique of molecular biology. A polymerase may be template dependent or template independent. Poly-A-polymerase is an example of template independent polymerase. Terminal deoxynucleotidyl transferase also known to have template independent and template dependent activities. DNA polymerase (DNA-directed DNA polymerase, DdDP) Family A: DNA polymerase I; Pol γ, θ, ν Family B: DNA polymerase II; Pol α, δ, ε, ζ Family C: DNA polymerase III holoenzyme Family X: Pol β, λ, μ Terminal deoxynucleotidyl transferase (TDT), which lends diversity to antibody heavy chains. Family Y: DNA polymerase IV (DinB) and DNA polymerase V (UmuD'2C) - SOS repair polymerases; Pol η, ι, κ Reverse transcriptase (RT; RNA-directed DNA polymerase; RdDP) Telomerase DNA-directed RNA polymerase (DdRP, RNAP) Multi-subunit (msDdRP): RNA polymerase I, RNA polymerase II, RNA polymerase III Single-subunit (ssDdRP): T7 RNA polymerase, POLRMT Primase, PrimPol RNA replicase (RNA-directed RNA polymerase, RdRP) Viral (single-subunit) Eukaryotic cellular (cRdRP; dual-subunit) Template-less RNA elongation Polyadenylation: PAP, PNPase Polymerases are generally split into two superfamilies, the "right hand" fold () and the "double psi beta barrel" (often simply "double-barrel") fold. The former is seen in almost all DNA polymerases and almost all viral single-subunit polymerases; they are marked by a conserved "palm" domain. The latter is seen in all multi-subunit RNA polymerases, in cRdRP, and in "family D" DNA polymerases found in archaea. The "X" family represented by DNA polymerase beta has only a vague "palm" shape, and is sometimes considered a different superfamily ().