Table 1. Variation in the 150- and 430-loops of N1 and N2 NA alleles of avian, swine and human influenza viruses.

Host	N1 and N2 alleles	N	150-loop			430-loop
			147	149	150	430	431	432
Swine N1	N1 swine H1N1 classic lineage consensus	158	G	V	K	Q	P	K
	N1 swine H1N1 Eurasian lineage consensus	165	G	I/V	K	R	P	K
Human N1	N1 human H1N1 2009 pandemic consensus and A/California/04/2009	1,806	G	I	K	R	P	K
	N1 human H1N1 seasonal 2007–2009 consensus	1,809	G	V	K	L	P	R
	N1 human H1N1 seasonal 1950–2007 consensus		G	V	K	R	P	R
	N1 human H1N1 seasonal 1930–40s consensus		G	V	K	R	P	K
	N1 human H1N1 1918 pandemic		G	V	K	Q	P	K
Avian N1	N1 avian consensus and A/Vietnam/1203/2004	2,141	G	V	K	R	P	K
Human N2	N2 human H3N2 seasonal mid-2000s-present consensus	1,727	N/D	V	R	R	K	E
	N2 human H3N2 seasonal 1990-mid 2000s consensus		D	V	H	R	K	Q/E
	N2 human H3N2 seasonal 1970–80s consensus		D	I	H	R	E	Q
	N2 human H3N2 1968 pandemic (NA of human H2N2 origin)		D	I	H	R	K	Q
	N2 human H2N2 seasonal A/Tokyo/3/1967 (atypical 149V)		D	V	H	R	K	Q
	N2 human H2N2 seasonal 1960s consensus	88	D	I	H	R	Q/K	Q
	N2 human H2N2 1957 pandemic (NA of avian origin)		G	I	H	R	P	Q
Avian N2	N2 avian polymorphisms seen since the mid-1990s	1,743	G	T/A/S	H	R	P	K/Q
	N2 avian consensus		G	I	H	R	P	Q

Consensus sequences contain amino acids at a frequency of at least 80%. Sequences in bold font correspond to structures simulated in this paper. Table entries are single-letter amino acid codes.