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J Bacteriol. 1974 June; 118(3): 928-934
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

Proline Excretion and Indirect Suppression in Escherichia coli and Salmonella typhimurium

Biological Sciences Group, The University of Connecticut, Storrs, Connecticut 06268

ABSTRACT

The last step in proline biosynthesis in Escherichia coli K-12, Salmonella typhimurium LT7, and a number of other enterobacterial isolates is regulated so that no proline is excreted, even if excess ¹-pyrroline-5-carboxylate, the immediate precursor of proline, is added to a culture. In proline auxotrophs blocked at an early step in proline biosynthesis (proA or proB), reversion to prototrophy is often due to a mutation in the arginine pathway which diverts N-acetyl glutamate -semialdehyde to proline synthesis, thus bypassing the proA or proB block. In such double mutants (proAB, argD), the last step in proline synthesis appears to be unregulated, since proline is excreted. Feedback inhibition and repression of the arginine pathway overcomes indirect suppression (restoring the Pro^– phenotype), but proline regulation is not restored; double mutants still excrete proline when fed ¹-pyrroline-5-carboxylate exogeneously. A new class of proline analogue-resistant mutant, due to mutation at argD, is also described.

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