Biochem/physiol Actions

The carboxy-terminal repeat domain (CTD) of the largest subunit of RNA pol II contains tandem repeats of a heptapeptide sequence Tyr-Ser-Pro-Thr-Ser-Pro-Ser which is highly conserved among eukaryotic organisms. There are two forms of RNA pol II in vivo: IIO, which is extensively phosphorylated at the CTD, and IIA, which is not phosphorylated. The IIA form preferentially enters the pre-initiation complex (PIC), whereas IIO is found in the elongation complex. The kinase activity of TFIIH can mediate CTD phosphorylation, although other kinases, including Cdc2, Ctk1, the Srb10-Srb11 kinase-cyclin pair, and P-TEFb, have also been implicated in CTD phosphorylation. A phosphatase responsible for the dephosphorylation of the CTD has also been identified. CTD phosphatase activity is regulated by TFIIB and TFIIF. The CTD has also been implicated in pre-mRNA processing, most likely functioning as a platform for the recruitment and assembly of factors involved in pre-mRNA processing.

The CTD works as a binding scaffold for nuclear factors through its phosphorylation. It is suggested to be also involved in chromatin structure modification, DNA damage/repair, protein degradation and synthesis, RNA degradation, snRNA (small nuclear RNA) modification, and snoRNP (small nucleolar ribonucleoprotein) biogenesis.

Physical form

Clear and colorless frozen liquid solution

Preparation Note

Use a manual defrost freezer and avoid repeated freeze-thaw cycles. While working, please keep sample on ice.