ATAC B Complex ATAC A Complex U4 ATAC:U5:U6 ATAC Complex Formation of AT-AC B Complex Authored: Joshi-Tope, G, 2003-10-27 22:47:00 Reactome Database ID Release 4375081 Reactome, http://www.reactome.org ReactomeREACT_1253 The U4atac/U6atac enters the spliceosome and U6atac snRNA forms base pairing interactions with the 5' ss and also forms base pairing interactions with U12 and U4atac is partially displaced. U5 snRNP, the only snRNP common to both the major and minor splicing pathways, also joins the spliceosome to form the B complex and interacts with nucleotides within the 3' end of the exon flanking the 5' ss.