PathwayStep1 PathwayStep2 PathwayStep3 PathwayStep4 PathwayStep5 PathwayStep6 PathwayStep7 PathwayStep8 PathwayStep9 Formation of cap binding complex (CBC) Recognition and binding of the mRNA cap by the cap-binding complex Methylation of GMP-cap by RNA Methyltransferase Dissociation of transcript with 5'-GMP from GT Transfer of GMP from the capping enzyme GT site to 5'-end of mRNA Formation of the CE:GMP intermediate complex Hydrolysis of the 5'-end of the nascent transcript by the capping enzyme Capping complex formation Activation of GT RNA Polymerase II CTD (phosphorylated) binds to CE SPT5 subunit of Pol II binds the RNA triphosphatase (RTP) mRNA Capping GENE ONTOLOGYGO:0006370 Pubmed10395561 Pubmed11017188 Pubmed11909521 Pubmed3326038 Reactome Database ID Release 4372086 Reactome, http://www.reactome.org ReactomeREACT_1470 The 5'-ends of all eukaryotic pre-mRNAs studied thus far are converted to cap structures. The cap is thought to influence splicing of the first intron, and is bound by 'cap-binding' proteins, CBP80 and CBP20, in the nucleus. The cap is important for translation initiation, and it also interacts with the poly(A)terminus, via proteins, resulting in circularization of the mRNA to facilitate multiple rounds of translation. The cap is also important for mRNA stability, protecting it from 5' to 3' nucleases, and is required for mRNA export to the cytoplasm.<BR>The capping reaction usually occurs very rapidly on nascent transcripts; after the synthesis of only a few nucleotides by RNA polymerase II. The capping reaction involves the conversion of the 5'-end of the nascent transcript from a triphosphate to a diphosphate by a RNA 5'-triphosphatase, followed by the addition of a guanosine monophosphate by the mRNA guanylyltransferase, to form a 5'-5'-triphosphate linkage. This cap is then methylated by 2'-O-methyltransferases.<P> PathwayStep11 PathwayStep10