Spliceosomal E Complex capped, methylated pre-mRNP:CBC complex U1 snRNP CC1.3 protein /3 RRM, RS UBA, Tudor - FLJ21007 SMC2 (P-loop, DA-box) ASR2B DnaJ hom. NP_055602 p68 DEAH protein hPrp19 HuR /3 RRM protein NFAR-2 protein Formation of the Spliceosomal E complex Pre-mRNA transcripts become rapidly associated with many RNA-binding proteins, including hnRNP proteins, cap-binding proteins, SR proteins, etc; in the test tube this binding does not require splice sites or ATP. The E complex, or early complex, is the first detectable functional intermediate in spliceosome assembly in vitro. It is an ATP-independent complex. When a functional 5' splice site is present, it is bound by the U1 snRNP. The splicing factor U2AF (65 and 35 kDa subunits) binds to the polypyrimidine tract (Y)n and the AG dinucleotide at the 3' splice site, respectively. SF1/mBBP binds to the branch site. Binding of many of these factors is cooperative; e.g., SR proteins and U2AF apparently interact with each other, facilitating their binding to the pre-mRNA. In the presence of ATP, the E complex is converted to the first ATP-dependent spliceosomal complex, namely the A complex. Pubmed12176931 Pubmed12477934 Reactome Database ID Release 4372107 Reactome, http://www.reactome.org ReactomeREACT_222