The lactose system inKlebsiella aerogenesV9A 2. Galactoside permeases which accumulate lactose or melibiose

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Abstract
Klebsiella aerogenes V9A possesses at least three galactoside permeases, the lactose permease (LacP), the melibiose permease (MelP) and a third permease (GPIII), and also a galactose permease. It is shown that the first three of these permeases all accumulate both lactose and melibiose efficiently, while the galactose permease takes up neither sugar. Lactose only induces LacP and melibiose only induces MelP. d-fucose, isopropyl-β-d-thiogalactoside (IPTG) and methyl-β-d-thiogalactoside (TMG) all induce GPIII, but galactose does not. GPIII takes up both lactose and melibiose but cannot accumulate lactose in the presence of IPTG. Thus substantial differences are found between the galactoside permeases of Klebsiella and Escherichia coli.