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The gene xylE, coding for xylose-proton symport in Escherichia coli, was cloned and its DNA sequence determined. The cloning strategy utilized lambda placMu insertions and exploited the proximity of xylE to malB. A 2.8-kilobase HincII fragment of cloned DNA restored 14Cxylose transport and xylose-proton symport activities to a xylose transport-negative strain. The xylE gene was identified as a 1473-base pair open reading frame, located 373 base pairs downstream of malG, encoding a hydrophobic protein of Mr 53,607. The amino acid sequence of XylE bore little resemblance to the lactose-proton LacY symporter or melibiose-sodium MelB symporter, but a high degree of homology was found with the arabinose-proton AraE symporter of E. coli and glucose transport proteins of mammals. Structural analyses and comparisons suggest that 12 membrane-spanning segments may occur in the XylE protein.
Davis et al. (Thu,) studied this question.