HA-tag

Human influenza hemagglutinin (HA) is a surface glycoprotein required for the infectivity of the human virus. The HA tag is derived from the HA-molecule corresponding to amino acids 98-106. It has been extensively used as a general epitope tag in expression vectors. Many recombinant proteins have been engineered to express the HA tag, which does not appear to interfere with the bioactivity or the biodistribution of the recombinant protein. This tag facilitates the detection, isolation, and purification of the protein of interest.

The HA tag is not suitable for detection or purification of proteins from apoptotic cells since it is cleaved by Caspase-3 and / or Caspase-7 after its sequence DVPD, causing it to lose its immunoreactivity.

The actual HA tag is as follows: 5' TAC CCA TAC GAT GTT CCA GAT TAC GCT 3' or 5' TAT CCA TAT GAT GTT CCA GAT TAT GCT 3'

The amino acid sequence is: YPYDVPDYA

...
Wikipedia