An RNA-dependent ATPase associated with U2/U6 snRNAs in pre-mRNA splicing

THE hydrolysis of ATP by a group of RNA-dependent ATPases (DEAD/H proteins 1 ) is required for spliceosome assembly, but not for the subsequent transesterification reactions 2 . Little is known about the function of these ATPases in relation to the RNA conformational changes that occur in formation of active structures, in which U2/U6 small nuclear RNA (snRNA) interactions 3,4 are essential for splicing to take place. Using a synthetic lethal genetic screen, we have isolated four yeast splicing factors involved in U2/U6 snRNA interactions (D.X. et al ., manuscript in preparation). The RNA-dependent ATPase activity associated with one such factor, the Slt22 protein, is stimulated preferentially by annealed U2/U6 snRNAs. Both mutant slt22-1 and U2 snRNA cause a reduction in stimulation. The slt22-1 mutation blocks splicing at or before the first step, resulting in the accumulation of an unusual complex which lacks U5 snRNA. Our results indicate that the U2/U6 snRNA interactions facilitated by Slt22 are also involved in the interaction of U5 snRNA with the spliceosome.