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J Bacteriol. 1971 June; 106(3): 983-993
Copyright © 1971 American Society for Microbiology. All Rights Reserved.

Minor Threonine Dehydratase Encoded Within the Threonine Synthetic Region of Bacillus subtilis¹

^a Department of Microbiology, University of Miami, School of Medicine, Miami, Florida 33152
Department of Biochemistry, University of Miami, School of Medicine, Miami, Florida 33152

ABSTRACT

Challenging auxotrophs on metabolites that are precursors of a biosynthetic step involving a mutated enzyme has revealed a new class of suppressor mutations which act by derepressing a minor enzyme activity not normally detected in the wild-type strain. These indirect, partial suppressor mutations which allow isoleucine auxotrophs to grow on homoserine or threonine have been analyzed to determine their effect on enzymes involved in the biosynthesis of these amino acids. It has been found that one class of these suppressor mutations (sprA) leads to the derepression of homoserine kinase, homoserine dehydrogenase, and a minor threonine dehydratase that is not sufficiently active to be detected in the wild-type strain. The gene encoding this second threonine dehydratase activity has been found to be located between the structural genes for homoserine kinase and homoserine dehydrogenase. The results of these experiments indicate that plating of auxotrophs on precursors of a biosynthetic step involving mutated enzymes could prove to be a valuable method for the detection of regulatory mutants as well as a possible tool in studying the evolution of biochemical pathways.

² Present address: Department of Microbiology, Yale University, New Haven, Conn. 06520.

¹ This report is part of a thesis presented by D. Vapnek to the University of Miami in partial fulfillment of the requirement for a Ph.D. degree.