Identification of two catalytic subunits of tRNA splicing endonuclease from Arabidopsis thaliana

tRNA splicing endonuclease is essential for the correct removal of introns from precursor tRNA molecules of Archaea and Eucarya. The only well-charact erized eucaryotic enzyme until now is the endonuclease from yeast (Saccharo myces cerevisiae). This protein has a heterotetrameric structure. Two of th e four subunits, i.e. Sen34 and Sen44, contain the active sites for cleavag e at the 3'- and 5'-splice sites, respectively. We have identified three no vel genes from Arabidopsis thaliana, encoding putative subunits of tRNA spl icing endonuclease. They are designated as AtSen1, AtSen2, and AtpsSen1. Bo th genes AtSen1 and AtSen2 seem to be functionally active, as deduced from corresponding cDNA sequences. Comparison of the amino acid sequences of the these two Arabidopsis proteins revealed 72% identity. However, AtpsSen1 is more similar to AtSen1, but is very likely a pseudogene, as concluded from extended stretches of deletions and the presence of in-frame stop codons. All putative proteins contain a conserved domain at their C-terminus common to counterparts from other organisms. Interestingly, they are more similar to the yeast catalytic subunit Sen44 than to Sen34. Southern analysis with various probes revealed that each gene is present as single copies in the nuclear genome. The evolutionary implications of these findings are discuss ed. (C) 2000 Elsevier Science B.V. All rights reserved.