SUPPRESSOR U1 SNRNAS IN DROSOPHILA

Although the role of U1 small nuclear RNAs (snRNAs) in 5' splice site recognition is well established, suppressor U1 snRNAs active in intact multicellular animals have been lacking. Here we describe suppression of a 5' splice site mutation in the Drosophila melanogaster white gen e (w(DR18)) by compensatory changes in U1 snRNA. Mutation of positions -1 and +6 of the 5' splice site of the second intron (ACG I GTGAGT to ACCIGTGAGC) results in the accumulation of RNA retaining this 74-nucl eotide intron in both transfected cells and transgenic flies. U1-3G, a suppressor U1 snRNA which restores base-pairing at position +6 of the mutant intron, increases the ratio of spliced to unspliced w(DR18) RN A up to fivefold in transfected Schneider cells and increases eye pigm entation in w(DR18) flies. U1-9G, which targets position-1, suppresses w(DR18) in transfected cells less well. U1-3G,9G has the same effect as U1-3G although it accumulates to lower levels. Suppression of w(DR1 8) has revealed that the U1b embryonic Variant (G134 to U) is active i n Schneider cells and pupal eye discs. However, the combination of 9G with 134U leads to reduced accumulation of both U1b-9G and U1b-3G,9G, possibly because nucleotides 9 and 134 both participate in a potential long-range intramolecular base-pairing interaction. High levels of fu nctional U1-3G suppressor reduce both viability and fertility in trans formed flies. These results show that, despite the difficulties inhere nt in stably altering splice site selection in multicellular organisms , it is possible to obtain suppressor U1 snRNAs in flies.