Analysis of Melibiose Mutants Deficient in α-Galactosidase and Thiomethylgalactoside Permease II in Escherichia coli K-12

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Abstract
Three types of mutants (mel") unable to metabolize the a-D-galactoside, melibiose, were derived from E. coli K-12. One type lacked a -galactosidase; another lacked a specific transport system, termed thiomethylgalactoside (TMG) permease II; and the 3rd lacked both of these functions. The mutational sites were genetically mapped by recombination frequency with different markers and by determination of chromosomal transfer in interrupted-mating experiments. All three mel" mutant types mapped in a cluster near to the metA marker on the E. coli chromosome and were cotransducible. Induction studies revealed that the 3 [alpha] -D-galactosides, melibiose, melibiitol, and galactinol, induced a-galactosidase and TMG permease II corrdinately; D-galactose also induced them but only in a galactokinaseless mutant. These data suggest that [alpha] -galactosidase and TMG permease II may be components of a common operon.

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