A novel base-pairing interaction between U2 and U6 snRNAs suggests a mechanism for the catalytic activation of the spliceosome.
Prior to the chemical steps of mRNA splicing, the extensive base-pairing interaction between the U4 and U6 spliceosomal snRNAs is disrupted. Here, we use a mutational analysis in yeast to demonstrate a conserved base-pairing interaction between the U6 and U2 snRNAs that is mutually exclusive with the U4-U6 interaction. In this novel pairing, conserved sequences in U6 interact with a sequence in U2 that is immediately upstream of the branch point recognition region. Remarkably, the residues in U6 that can be consequently juxtaposed with the intron substrate include those that have been proposed previously to be catalytic. Both the first and second steps of splicing are inhibited when this base-paired structure is mutated. These observations, together with the high conservation of the U2-U6 structure, lead us to propose that it might be a component of the spliceosomal active site.
Madhani
H D
HD
Department of Biochemistry and Biophysics, University of California, San Francisco 94143.
Guthrie
C
C
D001483:Base Sequence; D005816:Genetic Complementation Test; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D012326:RNA Splicing; D012331:RNA, Fungal / Q000235:genetics; D012342:RNA, Small Nuclear / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D017381:Spliceosomes / Q000378:metabolism*; D013329:Structure-Activity Relationship
D012331:RNA, Fungal; D012342:RNA, Small Nuclear