RNA STRUCTURAL PATTERNS AND SPLICING - MOLECULAR-BASIS FOR AN RNA-BASED ENHANCER

Efficient splicing of the 325-nt yeast (Saccharomyces cerevisiae) rp51 b intron requires the presence of two short interacting sequences loca ted 200 nt apart. We used the powerful technique of randomization-sele ction to probe the overall structure of the intron and to investigate its role in pre-mRNA splicing. We identified a number of alternative R NA-RNA interactions in the intron that promote efficient splicing, and we showed that similar base pairings can also improve splicing effici ency in artificially designed introns. Only a very limited amount of s tructural information is necessary to create or maintain such a mechan ism. Our results suggest that the base pairing contributes transiently to the spliceosome assembly process, most likely by complementing int eractions between splicing factors. We propose that splicing enhanceme nt by structure represents a general mechanism operating in large yeas t introns that evolutionarily preceded the protein-based splicing enha ncers of higher eukaryotes.