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. [Display omitted] •U6 snRNA is pseudouridylated during filamentous growth•Pus1p catalyzes this modification•Constitutive U6 pseudouridylation stimulates filamentous growth•Inability to pseudouridylate U6 inhibits filamentous growth Pseudouridines (Ψ) are C5-glycoside isomers of uridine. Although they are implicated in enhanced local RNA stacking or altered protein-RNA interactions, their physiologic effects are mostly unknown. Here, Basak and Query report a Pus1p-dependent pseudouridine residue (U6-Ψ28) that is induced in the Saccharomyces cerevisiae spliceosome during filamentous growth, a morphogenic switch that occurs in response to environmental stress. They show that Pus1p-dependent pseudouridylation of U6 snRNA contributes to the filamentation growth program.