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J Bacteriol. 1974 February; 117(2): 517-526
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

Properties of Mutants in Galactose Taxis and Transport

Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, Wisconsin 53706
Department of Genetics, College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, Wisconsin 53706

ABSTRACT

ß-Methylgalactoside (mgl) permease mutants of Escherichia coli, which are defective in three genes, mglA, mglB, and mglC, were assayed for galactose taxis and galactose transport. The mglB product is the galactose-binding protein. Previous evidence, supported by our new findings, shows that the galactose-binding protein is the recognition component for galactose taxis as well as for galactose transport. Most mutants defective in mglB showed strong effects on both chemotaxis and transport; however, a couple showed effects chiefly on one process or the other, thus allowing a separation of chemotaxis and transport. The mglA and mglC products have not yet been identified, but they must be components of the galactose transport machinery since mutants defective in mglA or mglC, or both, showed strongly reduced transport. Although some of these mutants showed little chemotaxis, most gave close to wild-type chemotactic responses. Thus, transport is not required for galactose taxis. The bacteria detect changes in the fraction of binding protein associated with galactose, not changes in the rate of transport.

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