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J Gen Microbiol. 1992 Apr;138(4):693-9.

Analysis of the mutant proBA operon from a proline-producing strain of Serratia marcescens.

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Research Laboratory of Applied Biochemistry, Tanabe Seiyaku Co. Ltd., Osaka, Japan.


The nucleotide sequence of the proBA operon from a proline-hyperproducing mutant of Serratia marcescens was determined. Two base substitutions were found: one in the proB structural gene, coding for gamma-glutamyl kinase (GK), and a second one in the promoter region of the operon. The former base substitution led to a change of the predicted amino acid at position 117 from an alanine to a valine in GK. This mutation rendered GK 700-fold less sensitive to proline-mediated feedback inhibition than the wild-type enzyme. The other base substitution, a transversion from a G-C to an A-T, was located in the spacer region between the '-35' and '-10' sequences of the promoter, and it increased the transcriptional activity of this operon fourfold. Both these two base substitutions, which were acquired at the step of selecting mutants resistant to a toxic proline analogue, 3,4-dehydroproline, confer upon cells a high proline productivity and an increased osmotolerance.

[Indexed for MEDLINE]

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