The FF domains of yeast U1 snRNP protein Prp40 mediate interactions with Luc7 and Snu71.

The FF domain is conserved across all eukaryotes and usually acts as an adaptor module in RNA metabolism and transcription. Saccharomyces cerevisiae encodes two FF domain proteins, Prp40, a component of the U1 snRNP, and Ypr152c, a protein of unknown function. The structure of Prp40, its relationship to other proteins within the U1 snRNP, and its precise function remain little understood. Here we have investigated the essentiality and interaction properties of the FF domains of yeast Prp40. We show that the C-terminal two FF domains of Prp40 are dispensable. Deletion of additional FF domains is lethal. The first FF domain of Prp40 binds to U1 protein Luc7 in yeast two-hybrid and GST pulldown experiments. FF domains 2 and 3 bind to Snu71, another known U1 protein. Peptide array screens identified binding sites for FF1-2 within Snu71 (NDVHY) and for FF1 within Luc7 (phi[FHL] x [KR] x [GHL] with phi being a hydrophobic amino acid). Prp40, Luc7, and Snu71 appear to form a subcomplex within the yeast U1snRNP. Our data suggests that the N-terminal FF domains are critical for these interactions. Crystallization of Prp40, Luc7, and Snu71 have failed so far but co-crystallization of pairs or the whole tri-complex may facilitate crystallographic and further functional analysis.