
thumb|right|200px|A simple gravity flow column for Ni2+-affinity chromatography. The sample and subsequent buffers are manually poured into the column and collected at the bottom end after flowing through the resin bed (in light blue at the base of the column).
thumb|right|200px|A simple gravity flow column for Ni2+-affinity chromatography. The sample and subsequent buffers are manually poured into the column and collected at the bottom end after flowing through the resin bed (in light blue at the base of the column).
A polyhistidine-tag, best known by the trademarked name His-tag, is an amino acid motif in proteins that typically consists of at least six histidine (His) residues, often at the N- or C-terminus of the protein. It is also known as a hexa histidine-tag, 6xHis-tag, or His6 tag. The tag was invented by Roche, although the use of histidines and its vectors are distributed by Qiagen. Various purification kits for histidine-tagged proteins are commercially available from multiple companies.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).