Epitope tag technique has widely been accepted technique that fuses an epitope peptide to a certain protein as a marker for gene expression. With this technique, the gene expression can be easily monitored on western blotting, immunoprecipitation, and immunofluorescence, utilizing with an antibody that recognizes such an epitope. HA-tag (YPYDVPDYA) sequence is widely used for the epitope tag, which corresponding to the partial peptide of Influenza hemagglutinin protein.