Protein-RNA interactions in the U5 snRNP of Saccharomyces cerevisiae (vol 4, pg 1239, 1998)

We present here the first insights into the organization of proteins on the RNA in the Us snRNP of Saccharomyces cerevisiae. Photo-crosslinking with u niformly labeled U5 RNA in snRNPs reconstituted in vitro revealed five cont acting proteins, Prp8p, Snu114p, p30, p16, and p10, contact by the three sm aller proteins requiring an intact Sm site. Site-specific crosslinking show ed that Snu114p contacts the 5' side of internal loop 1, whereas Prp8p inte racts with five different regions of the 5' stem-loop, but not with the Sm site or 3' stem-loop. Both internal loops in the 5' domain are essential fo r Prp8p to associate with the snRNP, hut the conserved loop 1 is not, altho ugh this is the region to which Prp8p crosslinks most strongly. The extensi ve contacts between Prp8p and the 5' stem-loop of U5 RNA support the hypoth esis that, in spliceosomes, Prp8p stabilizes loop l-exon interactions. More over, data showing that Prp8p contacts the exons even in the absence of loo p 1 indicate that Prp8p may be the principal anchoring factor for exons in the spliceosome. This and the close proximity of the spliceosomal transloca se, Snu114p, to U5 loop 1 and Prp8p support and extend the proposal that Sn u114p mimics U5 loop 1 during a translocation event in the spliceosome.