Polymerases are enzymes which polymerize new DNA or RNA using an existing DNA or RNA template. Polymerases are essential in DNA replication and transcription.

PARPS  See outline

Tankyrasses (TANKs)

TANKs were identified as components of the human telemeric complex. They have also been proposed to have a role in vesicale trafficking and may serve as scaffolds for proteins involved in various other cellular processes. TANks are (ADP-ribose) transferases with some features of both signalling and cytoskeletal proteins. They contain the PARP domain, which catalyses poly-ADP-ribosylation of substrate proteins, the sterile alpha motif, which is shared with certain signalling molecules and the ANK domain, which contains 24 ankyrin repeats homologues to the cytoskeletal protein anykyrin. The ANK domain interacts with a telomeric protein, Telomere Repeat binding Factor-1 (TRF-1). These proteins were thus named TRF1-interacting ankyrin-related ADP-ribose polymerase (TANKs).

Functions: One of the more specific functions of TANK is the ADP-ribosylation of TRF-1. Human telomer function requires two telomere specific DNA binding proteins, TRF-1 and TRF-2. TRF-2 protecs chomosome ends and FR-1 regualtes telomere lenght. ADP ribosylation inhibits the ability of TRF-1 to bind to telomeric DNA. This poly-ADP-ribosylation of TRF-1 releases TRF-1 from the telomeres, opening up the telomeric complex and allow acces to telomerase. Thus, TANK functions as a positive regulator of telomere lenght, allowing elongation of the telomeres by telomerase.  

Members: Tankyrases (TANKs) members include TANK-1, TANK-2 and TANK-3.

Telomerase

Telomerase is a ribonucleoprotein responsible for the template independent synthesis of telomeric DNA. Human telomerase is made up of two components: (1) an essential structural RNA (TER) (wehre the human component is referred to as hTER), and (2) a catalytic protein (telomerase reverse transcriptase or TERT) (wehre the human component is referred to in the art as hTERT).

Telomerase works by recognizing the 3′ end of DNA, e.g., telomeres, and adding multiple telomeric repeats to its 3′ end with the catalytic protein component (e.g., hTERT) which has polymerase activity, and hTER which serves as the template for nucleotide incorporation. Telomerase recognizes the tip of a G rich strand of an existing telomere DNA repeat sequence on the parental strand and elongates it. The telomerase is able to do an RNA template that is a component of the enzyme itself (much like the reverse transcriptases of viruses). After extension of the parental strand by telomerase, replication of the lagging strand can be completed. The replication is such though that the parental strand still protrudes out since all of the extended parental strand is not replicated. This protrusion loops back to tuck its singlestranded terminus into the duplex DNA of the telomeric repeat sequence creating a unique structure which protects it from degradative enzymes.

Telomerase is also important in aging.