Cryoelectron Microscopy; Saccharomyces cerevisiae; Spliceosomes/chemistry; Spliceosomes/ultrastructure; Base Sequence; Biocatalysis; Catalytic Domain; Introns/genetics; Models, Biological; Models, Molecular; Nuclear Proteins/chemistry; Nuclear Proteins/metabolism; Protein Binding; Protein Domains; Protein Stability; RNA Helicases/chemistry; RNA Helicases/metabolism; RNA Helicases/ultrastructure; RNA Precursors/genetics; RNA Precursors/metabolism; RNA Precursors/ultrastructure; RNA Splice Sites/genetics; RNA Splicing; RNA Splicing Factors/chemistry; RNA Splicing Factors/metabolism; RNA, Small Nuclear/chemistry; RNA, Small Nuclear/metabolism; Ribonucleoprotein, U2 Small Nuclear/chemistry; Ribonucleoprotein, U2 Small Nuclear/metabolism; Ribonucleoprotein, U4-U6 Small Nuclear/chemistry; Ribonucleoprotein, U4-U6 Small Nuclear/metabolism; Ribonucleoprotein, U5 Small Nuclear/chemistry; Ribonucleoprotein, U5 Small Nuclear/metabolism; Ribonucleoproteins, Small Nuclear/chemistry; Ribonucleoproteins, Small Nuclear/metabolism; Saccharomyces cerevisiae/chemistry; Saccharomyces cerevisiae/genetics; Saccharomyces cerevisiae Proteins/chemistry; Saccharomyces cerevisiae Proteins/metabolism; Saccharomyces cerevisiae Proteins/ultrastructure; Spliceosomes/metabolism