Figure 1.

Location of the thioredoxin binding domain (TBD) in T7 and Klenow–TBD DNA polymerases. (Right) The x-ray crystal structure of Klenow DNA polymerase is shown (10), modeled using the program setor (11). (Left) The alignment of the H–H₁ region in T7 DNA polymerase and E. coli DNA polymerase I is shown (7). The unique 76-residue region in T7 DNA polymerase, located between helices H and H₁, is indicated by the dark rectangle. In the chimeric Klenow–TBD DNA polymerase, this domain has been inserted at the tip of the thumb with the deletion of seven residues from E. coli DNA polymerase, as indicated by the arrow.