uridyltransferase

Uridyltransferase is an enzyme that catalyzes the transfer of uridine residues from uridine triphosphate (UTP) to an acceptor molecule, most commonly the 3' end of an RNA molecule. In RNA biology, enzymes with this activity are usually called terminal uridylyl transferases (TUTases). They are members of the nucleotidyltransferase superfamily.

TUTases are found across bacteria, archaea and eukaryotes, with distinct nuclear and cytoplasmic versions in eukaryotes. In eukaryotes, several well-characterized enzymes include TUT1, TUT4 and TUT7; in plants and fungi, similar enzymes such as URT1 and Cid1 perform analogous tasks. They can act distributively or processively to add short or long uridine tails to substrates.

A major role is 3' end uridylation of RNA, which regulates stability and maturation. In animals, LIN28 recruits TUT4/TUT7 to uridylate pre-let-7 microRNA, diverting it to degradation by 3'-5' exoribonucleases and blocking let-7 maturation. Uridylation can also mark mRNAs for decay via exosome pathways or, in certain contexts, influence RNA processing and translation.

Mechanistically, uridyltransferases recognize RNA substrates and couple UTP hydrolysis to the formation of phosphodiester bonds at the RNA 3' end. Structural diversity among TUTases underpins substrate specificity, cellular localization, and regulatory interactions.