Table 1. Key adaptive mutations in the influenza A virus viral polymerase subunits that enhance the replication, spread or pathogenicity of avian strains in mammalian cells, where known affects on replication or transcription are specified.

Subunit	Mutation	Affects	Ref.
PB1	L13P	cRNA synthesis	[66]
	S678N	RNA synthesis	[66]
	N375S	Pathogenicity, RNA synthesis	[65]
PB2	E627K	RNA synthesis, nuclear import	[67]
	H357N	Pathogenicity, RNA synthesis	[85]
	D701N	Pathogenicity cRNA, mRNA synthesis	[66]
	E677G	Pathogenicity, RNA synthesis	[81]
	T271A	Pathogenicity, RNA synthesis	[81]
	S714R	Pathogenicity, cRNA and mRNA synthesis	[66]
	G590S	Pathogenicity, RNA synthesis	[81]
	Q591R	Pathogenicity, RNA synthesis	[81]
PA	P400L	RNA synthesis	[84]
	T552S	Pathogenicity, RNA synthesis	[84]
	T85I	RNA synthesis	[82]
	G186S	RNA synthesis	[82]
	L336M	Pathogenicity, RNA synthesis	[82]
	A36T	RNA synthesis	[85]
	T97I	Pathogenicity, RNA synthesis	[83]
	K615N	Pathogenicity, vRNA synthesis	[66]

cRNA: Complementary RNA; PA: Polymerase acidic; PB1: Polymerase basic 1; PB2: Polymerase basic 2; vRNA: Viral RNA.