Insertions of codons encoding basic amino acids in H7 hemagglutinins of influenza A viruses occur by recombination with RNA at hotspots near snoRNA binding sites

MBCS amino acid sequences in H7 HA RNAs yielded by recombination (Khatchikian et al. 1989; Orlich et al. 1994; Banks et al. 2001; Hirst et al. 2004; Suarez et al. 2004; Berhane et al. 2009; Iglesias et al. 2010; Maurer-Stroh et al. 2013; Lee et al. 2017; Beerens et al. 2020). Amino acids at eight positions upstream of the cleavage site (P1–P8) which could affect cleavage by furin-like proteases (Duckert et al. 2004) are shown, inserted amino acids are underlined. Important basic residues at positions P1, P2, P4, and P6 are highlighted, cleavage site is shown by arrow. For strain abbreviations, see Materials and Methods.