• Korean Journal of Microbiology
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• v.32 no.2
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• pp.109-114
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• 1994

The Escherichia coli aroA and serC genes constitute a mixed-function operon which involves in two different amino acid biosynthetic pathways. The regulation of expression of serC-aroA operon was evaluated through the use of a serC-araA-lacZ fusion plasmid pWH2. The expression of the serC-aroA operon was decreased by aromatic amino acids such as tyrosine, tryptophan, and phenylalanine. The repressible effects were diminished in E. coli tyrR of trpR strain, indicating the involvemnt of TyrR of TrpR protein in the repression. Tyrosine was competitie with cAMP in the influence on the expression of the serC-AroA operon. From these data, it was suggested that the serC-aroA operon is controlled by aromatic amino acids in a negative manner.

• BMB Reports
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• v.28 no.1
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• pp.21-26
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• 1995

The Escherichia coli mixed-function serC-aroA operon encodes biosynthethic enzymes for unrelated pathways leading to the syntheses of serine and aromatic amino acids. It has been proposed that the operon is expressed in a cAMP-dependent manner. In this work experiments were performed to investigate the cAMP-dependent expression of the operon. Exogenous cAMP increased ${\beta}$-galactosidase synthesis in the $cya^+$ and cya strains harboring the serC-aroA-lac fusion plasmid. This enhancement was more dramatic in the $cya^-$ strain grown in a minimal medium. In a dot blot assay the serC-aroA mRNA content increased in a concentration-dependent pattern after the addition of exogenous cAMP. The activity of phosphoserine aminotransferase, encoded by the serC gene, apparently increased in E. coli cells after the addition of cAMP. All results obtained confirmed that the expression of the E. coli serC-aroA operon is positively regulated by cAMP at the level of transcription.