U2 and U6 snRNA genes in the microsporidian Nosema locustae: evidence for a functional spliceosome.

The removal of introns from pre-messenger RNA is mediated by the spliceosome, a large complex composed of many proteins and five small nuclear RNAs (snRNAs). Of the snRNAs, the U6 and U2 snRNAs are the most conserved in sequence, as they interact extensively with each other and also with the intron, in several base pairings that are necessary for splicing. We have isolated and sequenced the genes encoding both U6 and U2 snRNAs from the intracellularly parasitic microsporidian Nosema locustae . Both genes are expressed. Both RNAs can be folded into secondary structures typical of other known U6 and U2 snRNAs. In addition, the N.locustae U6 and U2 snRNAs have the potential to base pair in the functional intermolecular interactions that have been characterized by extensive analyses in yeast and mammalian systems. These results indicate that the N.locustae U6 and U2 snRNAs may be functional components of an active spliceosome, even though introns have not yet been found in microsporidian genes.