pTWIN1 is an E. coli expression vector which can be used with the IMPACT™ Kit (NEB #E6901). pTWIN vectors are designed for protein purification or for the isolation of proteins with an N-terminal cysteine and/or a C-terminal thioester (1). A polylinker in the vector is designed for the in-frame fusion of a target gene between the modified Ssp DnaB (2) and Mxe GyrA inteins (3,4). The presence of the chitin binding domain from Bacillus circulans (5,6) facilitates purification. The double-stranded vector is 7,375 base pairs in length.