Removal of attenuator region of thr operon increases the production of threonine in Escherichia coli

Expression of the threonine (thr) operon of Escherichia coli is regulated by an attenuation mechanism. The regulatory portion of the thr operon contains a region coding for leader peptide that includes both consecutive threonine and isoleucine codons. Translation of the leader peptide controls the frequency of transcription termination at the attenuator site. The effect of attenuator region on the production of threonine by using the threonine overproducing strain E. coli HS528 was examined. The plasmids which caused an increase in the productivity were due to the destruction of secondary structure of mRNA around the attenuator located in the leader sequence. Among them, plasmids pEd9, pEd64, and pEd69 increased threonine production that was caused by disruption of the transcription terminator. E. coli HS528 cells harboring the plasmids gave 2–3 times more threonine than the host. These results indicated that the change in the secondary structure of mRNA in the leader sequence of the thr operon have an effect on the productivity of threonine in E. coli.