Mature intronless transcript derived mRNA with m7G cap removed vRNA Transcription Complex Initiated vRNA Transcription Complex Priming and Initiation of Transcription Authored: Bortz, E, Garcia-Sastre, A, 2007-02-12 19:39:05 EC Number: 2.7.7.48 GENE ONTOLOGYGO:0019083 Pubmed11296240 Pubmed6261960 Pubmed6269803 Pubmed7301581 Pubmed8107213 Pubmed8879132 Pubmed8955065 Pubmed9755184 Reactome Database ID Release 43168280 Reactome, http://www.reactome.org ReactomeREACT_6239 Reviewed: Squires, B, 2007-02-12 19:39:22 The host cell mRNA bound to viral RNA polymerase PB2 subunit is cleaved by the viral RNA polymerase PB1 subunit's endonuclease activity, and the capped 5' end plus 10-13 nucleotides of the host mRNA remains bound to the polymerase complex (Plotch, 1981; Krug, 1981; Hagen, 1994; Cianci, 1995, Li, 1998; Li, 2001). Viral mRNA may be protected against cap-snatching by the polymerase complex itself, which tightly binds capped viral mRNA (Shih, 1996). A guanine residue, complementary to a cytosine in the vRNA, is added to the host-derived cap, catalyzed by the RNA polymerase activity of the PB1 viral RNA polymerase subunit (Beaton, 1981; Toyoda, 1986).