Biochemical Mechanisms of Constitutive and Regulated Pre-mRNA Splicing

INTRODUCTION 560 SPLICING PATHWAy 560 THE PARADIGM: AUTOCATALYTIC SPLICING OF GROUP II INTRONS 560 SPLICEOSOME ASSEMBLY PATHWAY 561 The Vi snRNP-Binding Reaction ...... . ... . 563 The U2 snRNP-Binding Reaction 563 Entry of U4/U5/U6 snRNPs 565 Destabilization of V4 snRNA 565 THE SPLICING PROCESS 566 First Step and Catalysis 566 Second Step 566 mRNA Release, Spliceosome Disassembly, and Intron Degradation 567 U snRNPs 568 Sm-Binding Site , . . . . . . . . . . . . 568 Cap Structure , . . . . . . . . . . . . 569 snRN P Assembly 569 Structure-Function Analysis of Spliceosomal sRNAs 569 Higher Order snRNP-snRNP Interactions 574 NON-snRNP SPLICING FACTORS 574 Mammalian Factors , . . . . . . . . . . . . 574 Yeast Factors .. .... .. . .. .. 578 Protein Motifs in Splicing Factors 579 SELECTION OF SPLICE SITES 580 Splice Site Selection: A Hierarchy of Competition 581 Other Models 581