A FUNCTIONAL HOMOLOG OF A YEAST TRANSFER-RNA SPLICING ENZYME IS CONSERVED IN HIGHER EUKARYOTES AND IN ESCHERICHIA-COLI

tRNA splicing in the yeast Saccharomyces cerevisiae requires an endonu clease to excise the intron, tRNA ligase to join the tRNA half-molecul es, and 2'-phosphotransferase to transfer the splice junction 2'-phosp hate from ligated tRNA to NAD, producing ADP ribose 1 ''-2 '' cyclic p hosphate (Appr>p). We show here that functional 2'-phosphotransferases are found throughout eukaryotes, occurring in two widely divergent ye asts (Candida albicans and Schizosaccharomyces pombe), a plant (Arabid opsis thaliana), and mammals (Mus musculus); this finding is consisten t with a role for the enzyme, acting in concert with ligase, to splice tRNA or other RNA molecules. Surprisingly, functional 2'-phosphotrans ferase is found also in the bacterium Escherichia coli, which does not have any known introns of this class, and does not appear to have a l igase that generates junctions with a 2'-phosphate. Analysis of the da tabase shows that likely members of the 2'-phosphotransferase family a re found also in one other bacterium (Pseudomonas aeruginosa) and two archaeal species (Archaeoglobus fulgidus and Pyrococcus horikoshii). P hylogenetic analysis reveals no evidence for recent horizontal transfe r of the 2'-phosphotransferase into Eubacteria, suggesting that the 2' -phosphotransferase has been present there since close to the time tha t the three kingdoms diverged. Although 2'-phosphotransferase is not p resent in all Eubacteria, and a gene disruption experiment demonstrate s that the protein is not essential in E. coli, the continued presence of 2'-phosphotransferase in Eubacteria over large evolutionary times argues for an important role for the protein.