TABLE 2.

Alteration of the PB2 gene following virus propagation in CEF and OEF^a

Fibroblast type and passage no.	% Viral clones encoding a mammalian-type amino acid in the PB2 protein of the indicated H5N1 virus (no. of clones analyzed)
	A/duck/Vietnam/5001/2004		A/duck/Vietnam/ NCVD18/2004
	PB2-627Lys	PB2-701Asn	PB2-627Lys	PB2-701Asn
CEF
1	0 (6)	0 (6)	0 (8)	0 (8)
2	0 (6)	0 (6)	0 (8)	0 (8)
3	0 (14)	0 (14)	0 (8)	0 (8)
4	0 (6)	0 (6)	0 (6)	0 (6)
5	0 (6)	0 (6)	0 (6)	0 (6)
6	0 (11)	0 (11)	0 (10)	0 (10)
OEF
1	0 (8)	0 (8)	11.1 (9)	0 (6)
2	0 (8)	0 (8)	37.5 (8)	0 (6)
3	0 (8)	12.5 (8)	70.0 (10)	0 (6)
4	0 (6)	16.6 (6)	100 (6)	0 (6)
5	0 (6)	16.6 (6)	100 (6)	0 (6)
6	0 (10)	80.0 (10)	100 (10)	0 (10)

^aWe sequenced the PB2 gene of viruses grown in OEF or CEF at the indicated passage number and calculated the proportion of viruses possessing mammalian-type amino acids at positions 627 and 701 in PB2.