Identification of the GalP galactose transport protein of Escherichia coli.

Escherichia coli strains have been isolated with a transposon 10 insertion or an amber mutation inactivating the galP gene, which specifies the galactose-H+ (GalP) transport system. Comparison of the membrane proteins between these strains and their GalP+ parents by dual isotope analysis showed that a component of Mr = 34-39,000 was consistently absent from the GalP- mutants. Galactose, methyl-beta-D-galactoside, and talose protected the GalP transport system from inactivation by N-ethylmaleimide. A membrane protein of Mr = 34-38,000 was modified by N-([2-3H]ethyl)maleimide at the binding site of these sugars. Two-dimensional gel electrophoresis of the membrane proteins has resolved a component of Mr = 35-38,000 (average apparent pI = 5.7) present in parent strains (GalP+) but not in the GalP- mutants. These observations identified a protein of apparent Mr = 37,000 as the product of the galP gene of E. coli.