Expression of the metA gene of Escherichia coli K-12 in recombinant plasmids

The expression of the metA gene coding for the first enzyme in the methionine biosynthethic pathway was studied in wild-type and in deregulated strains of Escherichia coli K-12 carrying the gene on multicopy plasmids. We looked at (a) in vitro activity of the metA product-The enzyme homoserine transsuccinylase (HTS); (b) resistance of cells carrying metA plasmids to the analogue α-methylmethionine which specifically inhibits HTS, and (c) the metA polypeptide in mini cells. The results indicate that the M_r value of the polypeptide synthesized by the metA gene is 40 000. The synthesis of HTS, even when the metA gene is cloned on a multicopy plasmid, is under the negative control of the regulatory metJ gene.