Tpt1 catalyses the last step of tRNA splicing in yeast. It transfers the splice junction 2'-phosphate from ligated tRNA to NAD, to produce ADP-ribose 1"-2"-cyclic phosphate. This is presumed to be followed by a transesterification step to release the RNA. The first step of this reaction is similar to that catalysed by some bacterial toxins. E. coli KptA and mouse Tpt1 are likely to use the same reaction mechanism [1].

1: Transient ADP-ribosylation of a 2'-phosphate implicated in its removal from ligated tRNA during splicing in yeast. Spinelli SL, Kierzek R, Turner DH, Phizicky EM; J Biol Chem 1999;274:2637-2644. PMID:9915792