Molecular Cell Short Article trans-Splicing to Spliceosomal U2 snRNA Suggests Disruption of Branch Site-U2 Pairing during Pre-mRNA Splicing

SUMMARY Pairing between U2 snRNA and the branch site of spliceosomal introns is essential for spliceosome assembly and is thought to be required for the first catalytic step of splicing. We have identified an RNA comprising the 5 0 end of U2 snRNA and the 3 0 exon of the ACT1-CUP1 reporter gene, resulting from a trans-splicing reaction in which a 5 0 splice site-like sequence in the universally conserved branch site-binding region of U2 is used in trans as a 5 0 splice site for both steps of splicing in vivo. Formation of this product occurs in functional spliceosomes assembled on reporter genes whose 5 0 splice sites are predicted to bind poorly at the spliceosome catalytic center. Multiple spatially disparate splice sites in U2 can be used, calling into question both the fate of its pairing to the branch site and the details of its role in splicing catalysis

A Glimpse of the Catalytic Core of a Group II Intron

AbstractA paper in a recent issue of Science describes the first high-resolution structure of part of the catalytic core of a group II intron that will allow more detailed comparisons between the excision of introns by self-splicing group II introns and by nuclear pre-mRNA introns

A Pseudouridine Residue in the Spliceosome Core Is Part of the Filamentous Growth Program in Yeast

SummaryAlthough pseudouridine nucleobases are abundant in tRNAs, rRNAs, and small nuclear RNAs (snRNAs), they are not known to have physiologic roles in cell differentiation. We have identified a pseudouridine residue (Ψ28) on spliceosomal U6 snRNA that is induced during filamentous growth of Saccharomyces cerevisiae. Pus1p catalyzes this modification and is upregulated during filamentation. Several U6 snRNA mutants are strongly pseudouridylated at Ψ28. Remarkably, these U6 mutants activate pseudohyphal growth, dependent upon Pus1p, arguing that U6-Ψ28 per se can initiate at least part of the filamentous growth program. We confirmed this by using a designer small nucleolar RNA (snoRNA) targeting U6-U28 pseudouridylation. Conversely, mutants that block U6-U28 pseudouridylation inhibit pseudohyphal growth. U6-U28 pseudouridylation changes the splicing efficiency of suboptimal introns; thus, Pus1p-dependent pseudouridylation of U6 snRNA contributes to the filamentation growth program

A Pseudouridine Residue in the Spliceosome Core Is Part of the Filamentous Growth Program in Yeast

Although pseudouridine nucleobases are abundant in tRNAs, rRNAs, and small nuclear RNAs (snRNAs), they are not known to have physiologic roles in cell differentiation. We have identified a pseudouridine residue (Ψ28) on spliceosomal U6 snRNA that is induced during filamentous growth of Saccharomyces cerevisiae. Pus1p catalyzes this modification and is upregulated during filamentation. Several U6 snRNA mutants are strongly pseudouridylated at Ψ28. Remarkably, these U6 mutants activate pseudohyphal growth, dependent upon Pus1p, arguing that U6-Ψ28 per se can initiate at least part of the filamentous growth program. We confirmed this by using a designer small nucleolar RNA (snoRNA) targeting U6-U28 pseudouridylation. Conversely, mutants that block U6-U28 pseudouridylation inhibit pseudohyphal growth. U6-U28 pseudouridylation changes the splicing efficiency of suboptimal introns; thus, Pus1p-dependent pseudouridylation of U6 snRNA contributes to the filamentation growth program