Sm protein–Sm site RNA interactions within the inner ring of the spliceosomal snRNP core structure

摘要: Seven Sm proteins, E, F, G, D1, D2, D3 and B/B′, assemble in a stepwise manner onto the single-stranded site element (PuAU4–6GPu) of U1, U2, U4 U5 spliceosomal snRNAs, resulting doughnut-shaped core RNP structure. Here we show by UV cross-linking experiments using an RNA oligonucleotide (AAUUUUUGA) that several proteins contact RNA, with most efficient cross-links observed for G B/B′ proteins. Site-specific photo-cross-linking revealed distinct uridines (in first third positions, respectively) highly position-specific manner. Amino acids involved contacting are located at equivalent regions both namely loop L3 Sm1 motif, which has been predicted to jut into hole ring. Our results thus provide evidence that, within snRNP, multiple protein–Sm contacts occur on inner surface heptameric protein