Functional complementation of internal deletion mutants in the lactose permease of Escherichia coli.
Using the lactose permease of Escherichia coli, a well-characterized membrane protein with 12 transmembrane domains, we demonstrated that certain paired in-frame deletion constructs complement each other functionally. Although cells expressing the deletion mutants individually are unable to catalyze active lactose accumulation, cells simultaneously expressing specific pairs of deletions catalyze transport up to 60% as do cells expressing wild-type permease. Moreover, complementation clearly does not occur at the level of DNA but probably occurs at the protein level. Remarkably, functional complementation is observed only with pairs of permease molecules containing large deletions and is not observed with missense mutations or point deletions. Although the mechanism of functional complementation is obscure, the findings indicate that certain pairs of permease molecules containing specific internal deletions can interact to form a functional complex in the same way phenomenologically as do independently expressed polypeptides corresponding to different N- and C-terminal portions of the permease.
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Howard Hughes Medical Institute, Department of Physiology, University of California, Los Angeles 90024-1574.
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D000595:Amino Acid Sequence; D001483:Base Sequence; D001692:Biological Transport; D002872:Chromosome Deletion; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D005816:Genetic Complementation Test; D007785:Lactose / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D027981:Symporters
D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D009838:Oligodeoxyribonucleotides; D027981:Symporters; C021499:lactose permease; D007785:Lactose