Plasmids and Bacterial Strains. The E. coli bacterial strain LGS-322 (25), containing a chromosomal deletion in the wild-type mtlA gene, was used for the expression of EIImtl.Plasmids bearing the genes of the single-Trp mutants of EIImtl(W30, W42, W109, W117) (9) were used; the 5¢ regions of the genes were engineered to obtain EIImtl with an N-terminal thrombin-cleavable his-tag. Construction of the plasmid specifying the N-terminal his-tagged EIImtl will be published
elsewhere.