What does his tag stand for ? - (May/08/2001 )

His tag generally refers to 6 histidine residues present in a protein (usually fusion protein). These 6 histidines allow you to purify the "His tagged" protein by running it over a Nickel column or Nickelresin etc.(the histidine binds the Nickel and then you wash and elute with specific buffers) For more specific information call one of the companies that sells his tagged vectors or Nickel resins such as In Vitrogen.

I was wondering if it stands for a specific number of tagged histidines (6?) or simply for tagged histidines.