Towards understanding the catalytic core structure of the spliceosome.

The spliceosome catalyses the splicing of nuclear pre-mRNA (precursor mRNA) in eukaryotes. Pre-mRNA splicing is essential to remove internal non-coding regions of pre-mRNA (introns) and to join the remaining segments (exons) into mRNA before translation. The spliceosome is a complex assembly of five RNAs (U1, U2, U4, U5 and U6) and many dozens of associated proteins. Although a high-resolution structure of the spliceosome is not yet available, inroads have been made towards understanding its structure and function. There is growing evidence suggesting that U2 and U6 RNAs, of the five, may contribute to the catalysis of pre-mRNA splicing. In this review, recent progress towards understanding the structure and function of U2 and U6 RNAs is summarized.