Sandbox Reserved 329: Difference between revisions

Terminal uridylyl transferases (TUTases) belong to a superfamily of polymerase ß nucleotidyl transferases.<ref name="primary citation">PMID:17785418</ref> TUTases have been isolated from ''Trypanosoma brucei'' and also ''Leishmania'' ssp, parasites that cause diseases in humans such as African Sleeping Sickness.<ref>PMID:11893335</ref> TUTases can function in RNA editing; more specifically TUTase4 catalyzes a reaction that adds a nucleotide, from a nucleotide triphosphate, to uridine monophosphate (UMP), the minimally required terminal RNA substrate. (ref) TUTase4 is able to bind to the nucleotide triphosphates ATP, CTP, GTP or UTP, however, UTP and CTP are preferred, whereas ATP and GTP ligands have been shown to cause a significant decrease in enzymatic activity (ref). The preference for UTP causes TUTase4 to typically add a uracil nucleotide to the RNA substrate. This selectivity has a variety of mechanisms, including a loss of coplanarity (pi-electron stacking) between the ATP and a tyrosine of the active site (Y189) required for catalysis, and reduced stacking between the UMP and ATP rings. The RNA substrate in trypanosomal TUTases selects for cognate nucleosides and provides a metal ion binding site for Mg²⁺ ions required by the ligand.<ref name="primary citation">PMID:17785418</ref>