pTXB1 contains a mini-intein from the Mycobacterium xenopi gyrA gene (Mxe GyrA intein; 198 amino acid residues)  that has been modified to undergo thiol-induced cleavage at its N-terminus (3,5). The vector allows for the 
purification of a target protein without any extra amino acids by cloning into the NdeI and SapI sites. The target protein is fused at its C-terminus to a self-cleavable intein tag (~28 kDa) that contains the chitin 
binding domain (CBD, 6 kDa) allowing for affinity purification of the fusion precursor on a chitin column.