Meta-Biol

• Pathways

The DDX23 RNA helicase (homolog of yeast Prp28) binds ATP to dissociate the 5' splice site of the pre-mRNA from the U1 snRNA, causing displacement of the U1 snRNP from the spliceosome and allowing the 5' splice site to anneal with the U6 snRNA and the 5' exon with the U5 snRNA (Ismaili et al. 2001, Mohlmann et al. 2014, Boesler et al. 2016, Charenton et al. 2019). As annealing between the U6 snRNA and the 5' splice site proceeds, the U4 snRNA previously base-paired with the U6 snRNA becomes available to accommodate SNRNP200 (homolog of yeast Brr2) at the position where it will later dissociate the U4-U6 RNA duplex during subsequent activation. The B complex assembly is further stabilized by the recruitment of several B-specific proteins such as MFAP1, PRP38A, ZMAT2, and WBP4 (FBP21) whose roles have still to be precisely defined. The components of the Spliceosomal B complex have been ascertained using proteomic and structural methods (Rappsilber et al. 2002, Deckert et al. 2006, Bessonov et al. 2008, Wolf et al. 2009, Bessonov et al. 2010, Schmidt et al. 2014, Boesler et al. 2015, Zhang et al. 2018, Charenton et al. 2019, Kastner et al. 2019).