title: Insights into branch nucleophile positioning and activation from an orthogonal pre-mRNA splicing system in yeast.
abstract: The duplex formed between the branch site (BS) of a spliceosomal intron and its cognate sequence in U2 snRNA is important for spliceosome assembly and the first catalytic step of splicing. We describe the development of an orthogonal BS-U2 system in S. cerevisiae in which spliceosomes containing a grossly substituted second-copy U2 snRNA mediate the in vivo splicing of a single reporter transcript carrying a cognate substitution. Systematic use of this approach to investigate requirements for branching catalysis reveals considerable flexibility in the sequence of the BS-U2 duplex and its positioning relative to the catalytic center. Branching efficiency depends on the identity of the branch nucleotide, its position within the BS-U2 duplex, and its distance from U2/U6 helix Ia. These results provide insights into substrate selection during spliceosomal branching catalysis; additionally, this system provides a foundation and tool for future mechanistic splicing research.
authors.affiliation: The Rockefeller University, New York, NY 10065, USA.
authors.forename: Duncan J
authors.initials: DJ
authors.lastname: Smith
authors.forename: Maria M
authors.initials: MM
authors.lastname: Konarska
authors.forename: Charles C
authors.initials: CC
authors.lastname: Query
mesh_terms: D000818:Animals; D001483:Base Sequence; D006801:Humans; D007438:Introns; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D012322:RNA Precursors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D012326:RNA Splicing; D012342:RNA, Small Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017381:Spliceosomes / Q000235:genetics / Q000378:metabolism
chemical_list: D012322:RNA Precursors; D012342:RNA, Small Nuclear; D029701:Saccharomyces cerevisiae Proteins; C405484:U2 small nuclear RNA