RNA Polymerase II - C-terminus

C-terminus

The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal end, or COOH-terminus) of a protein or polypeptide is the end of the amino acid chain terminated by a free carboxyl group (-COOH). The convention for writing peptide sequences is to put the C-terminal end on the right and write the sequence from N- to C-terminus.

Each amino acid has a carboxyl group and an amine group, and amino acids link to one another to form a chain by a dehydration reaction by joining the amine group of one amino acid to the carboxyl group of the next. Thus polypeptide chains have an end with an unbound carboxyl group, the C-terminus, and an end with an amine group, the N-terminus. Proteins are naturally synthesized starting from the N-terminus and ending at the C-terminus.

The C-terminus can contain retention signals for protein sorting. The most common ER retention signal is the amino acid sequence -KDEL (or -HDEL) at the C-terminus, which keeps the protein in the endoplasmic reticulum and prevents it from entering the secretory pathway.

The C-terminus of proteins can be modified posttranslationally, for example, most commonly by the addition of a lipid anchor to the C-terminus that allows the protein to be inserted into a membrane without having a transmembrane domain. With Pol II, the C-terminus of RPB1 is appended to form the C-terminal domain (CTD).