Sequence encoding three copies of the hemagglutinin (HA) epitope YPYDVPDYA were fused in frame 3' to the single exon of the gene locus. A floxed neomycin cassette was inserted downstream of the exon and was later removed by breeding founders with a cre deleter strain. Mice homozygous for this C-terminal "tagged" allele recapitulated wild-type expression patterns of the endogenous protein. Protein function was unaltered as determined by phenotypic analysis. (J:151244)