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

Abstract

Three types of mutants ( mel − ) unable to metabolize the α- d -galactoside, melibiose, were derived from Escherichia coli K-12. One type lacked α-galactosidase; another lacked a specific transport system, termed thiomethylgalactoside (TMG) permease II; and the third 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 three α- d -galactosides, melibiose, melibiitol, and galactinol, induced α-galactosidase and TMG permease II coordinately; d -galactose also induced them but only in a galactokinaseless mutant. These data suggest that α-galactosidase and TMG permease II may be components of a common operon.