Asp-51 and Asp-120 are important for the transport function of the Escherichia coli melibiose carrier.
Asp-51 and Asp-120 of the Escherichia coli melibiose carrier on plasmid pKKMB were separately replaced by amber codons and transformed into eight amber suppressor strains, producing eight amino acid substitutions for each site. Glu-51 and Glu-120 were the only replacements in the carrier that allowed the cells to ferment melibiose and that showed transport of melibiose against a concentration gradient. Revertants to Glu-51 and Glu-120 show less activity than the wild type. The Asp-51 position is more crucial for Na(+)-stimulated melibiose accumulation than is the Asp-120 site.
Wilson
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Department of Cellular and Molecular Physiology, Harvard Medical School, Boston, Massachusetts 02115.
Wilson
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D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D001693:Biological Transport, Active; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000235:genetics*; D005285:Fermentation / Q000235:genetics; D008553:Melibiose / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D013489:Suppression, Genetic; D027981:Symporters
D026901:Membrane Transport Proteins; D027981:Symporters; C021548:melibiose permease; D008553:Melibiose