Enhanced and feedback-resistant γ-glutamyl kinase activity of anEscherichia colitransformant carrying a mutatedproBgene ofStreptococcus thermophilus

We used a PCR-based method to generate a single base pair mutation in the proB gene of Streptococcus thermophilus, which replaced an aspartic acid with a glycine residue at position 192 of the first proline biosynthetic enzyme gamma-glutamyl kinase. This was the first identified mutation in amino acid biosynthesis in S. thermophilus to our knowledge. The mutation caused an enhanced, feedback-resistant gamma-glutamyl kinase activity and conferred an analogue-resistant phenotype to an Escherichia coli transformant containing the mutated gene.