Spliceosomal Bact complex
spliceosomal bact complex
Although all snRNPs are present in the <a href=''>B complex</a>, it is still catalytically inactive and requires major conformational and compositional rearrangements (i.e., activation) in order to become competent to facilitate the first transesterification step of splicing. During spliceosome activation U1 and U4 are destabilized or released, giving rise to the activated spliceosome (i.e., the Bact complex). Subsequently, after a structural rearrangement is catalyzed by the DExH/D-box protein Prp2, the catalytically activated spliceosome (B* complex) is formed. The B* complex catalyses the first step of splicing, generating the cleaved 5' exon and intron-3' exon lariat intermediates, and at this stage the <a href=''>spliceosomal C complex</a> is generated.