pTXB1 is an E. coli expression vector in the IMPACT™ Kit (NEB #E6901) (1,2). It is designed for the in-frame insertion of a target gene into the polylinker upstream of the Mxe intein/chitin binding domain (27 kDa) (2,3,4,5). The fusion protein is bound to chitin beads and the thiol-induced cleavage activity of the intein releases the target protein. pTXB vectors are recommended for use in intein-mediated protein ligation and C-terminal labeling (2). This double stranded vector is 6,706 base pairs in length.