This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Bukhari, A. I. Articles by Taylor, A. L. Search for Related Content PubMed PubMed Citation Articles by Bukhari, A. I. Articles by Taylor, A. L.

 Previous Article  |  Next Article 

J Bacteriol. 1971 March; 105(3): 988-998
Copyright © 1971 American Society for Microbiology. All Rights Reserved.

Mutants of Escherichia coli with a Growth Requirement for Either Lysine or Pyridoxine¹

^a Department of Microbiology, University of Colorado Medical Center, Denver, Colorado 80220

ABSTRACT

Two distinct phenotypic classes of lysine requiring auxotrophs of Escherichia coli are described. Mutants of the LysA class produce little or no active diaminopimelic acid (DAP) decarboxylase and specifically require lysine for growth. Mutants of the LysB class produce a cryptic DAP decarboxylase which can be activated both in vivo and in vitro by higher than normal levels of its cofactor, pyridoxal 5'-phosphate. The LysB mutants have an alternate requirement for lysine or pyridoxine. Both LysA and LysB mutations map at 55 min, close to the thyA locus of E. coli. The association between pyridoxal phosphate and DAP decarboxylase appears to be much weaker in LysB mutants than in wild-type bacteria, and the mutant enzyme also sediments more slowly than wild-type enzyme in sucrose density gradients. The results suggest that the LysB mutations alter a specific region (or subunit) of the enzyme molecule which is needed to stabilize the binding of pyridoxal phosphate. These studies help to resolve certain contradictory observations on DAP decarboxylase reported earlier and may have relevance to pyridoxal phosphate enzymes in general. Prototrophic revertants of LysB mutants arise by second site mutations that result in increased availability of intracellular pyridoxal phosphate. These revertants appear to be derepressed for pyridoxine biosynthesis.

² Present address: Cold Spring Harbor Laboratory for Quantitative Biology, Cold Spring Harbor, New York 11724.

¹ This work was presented in part at the 69th Annual Meeting of the American Society for Microbiology, Boston, Mass., 26 April to 1 May 1970. Submitted in partial fulfillment of the requirement for Ph.D. degree at the Department of Microbiology, University of Colorado Medical Center.