SPECIFIC COMMITMENT OF DIFFERENT PREMESSENGER RNAS TO SPLICING BY SINGLE SR PROTEINS

HIGHER eukaryotic cells express a family of essential splicing factors with a characteristic RNA-binding domain and serine/arginine-rich (SR ) motif. These SR proteins, which include SC35(2-6) and SF2/ASF7-12, a re conserved from Drosophila to man, are required for early steps of s pliceosome assembly, and can influence splice-site selections. To addr ess their mechanisms of action, SR proteins were examined for their ro le in committing pre-messenger RNA to the splicing pathway. I report h ere that SC35 was sufficient on its own to form a committed complex wi th human beta-globin pre-mRNA. Examination of other SR proteins and pr e-mRNA substrates revealed that single SR proteins committed different pre-mRNAs to splicing with pronounced substrate specificity. These re sults suggest that splicing of different pre-mRNAs may require distinc t sets of SR proteins, and that the commitment by SR proteins may be a critical step at which alternative and tissue-specific splicing is re gulated.