Identification of the key site of 2457T ArgT (tyrosine residue in position 225) for the regulation of expression. ArgTDH5α over-expressed in 2457T (A) and in DH5α (B) could be detected either at 37°C or at 30°C. (C) The three corresponding different sites between the protein sequence of ArgT2457T and ArgTDH5α. (D) Comparison of ArgT over-expressed in four strains carrying different plasmids at 37°C and 30°C. The plasmids include pProEX-HTb-argT2457T (ArgT) and its site-mutated plasmids ArgTA16T, ArgTL38P and ArgTY225D. M: protein marker (Fermentas, UK).