GLY113-->ASP can restore activity to the ASP51-->SER mutant in the melibiose carrier of Escherichia coli.
ASP51 in the putative membrane-spanning helix 2 of the melibiose carrier of Escherichia coli was replaced by SER. This mutation caused failure of the cell to transport melibiose and failure to ferment melibiose on indicator plates. A melibiose-positive revertant was isolated from these plates and was found to have two additional mutations, GLY113-->ASP (in helix 4) and PHE16-->LEU (in helix 1). The double mutant ASP51-->SER/GLY113-->ASP was constructed and showed accumulation of melibiose. On the other hand ASP51-->SER/PHE16-->LEU showed no activity. It is concluded that the new carboxyl group at position 113 compensates for the loss of the carboxyl group at position 51.
Wilson
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DM
Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
Hama
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Wilson
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D000595:Amino Acid Sequence; D001224:Aspartic Acid / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics*; D005998:Glycine / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D012694:Serine / Q000378:metabolism*; D027981:Symporters
D026901:Membrane Transport Proteins; D027981:Symporters; D001224:Aspartic Acid; D012694:Serine; C021548:melibiose permease; D005998:Glycine