title: Melibiose permease and alpha-galactosidase of Escherichia coli: identification by selective labeling using a T7 RNA polymerase/promoter expression system.
abstract: Identification and selective labeling of the melibiose permease and alpha-galactosidase in Escherichia coli, which are encoded by the melB and melA genes, respectively, have been accomplished by selectively labeling the two gene products with a T7 RNA polymerase expression system [Tabor, S., & Richardson, C. C. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 1074]. Following generation of a novel EcoRI restriction site in the intergenic sequence between the two genes of the mel operon by oligonucleotide-directed, site-specific mutagenesis, melA and melB were separately inserted into plasmid pT7-6 of the T7 expression system. Expression of melB was markedly enhanced by placing a strong, synthetic ribosome binding site at an optimal distance upstream from the initiation codon of melB. Expression of cloned gene products was characterized functionally and by performing autoradiographic analysis on total cell, inner membrane, and cytoplasmic proteins from cells pulse labeled with (35S)methionine in the presence of rifampicin and resolved by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The results first confirm that alpha-galactosidase is a cytoplasmic protein with an Mr of 50K; in contrast, the membrane-bound melibiose permease is identified as a protein with an apparent Mr of 39K, a value significantly higher than that of 30K previously suggested [Hanatani et al. (1984) J. Biol. Chem. 259, 1807].
authors.affiliation: Laboratoire J. Maetz, Département de Biologie du Commissariat à l'Energie Atomique, Villefranche-sur-Mer, France.
authors.forename: T
authors.initials: T
authors.lastname: Pourcher
authors.forename: M
authors.initials: M
authors.lastname: Bassilana
authors.forename: H K
authors.initials: HK
authors.lastname: Sarkar
authors.forename: H R
authors.initials: HR
authors.lastname: Kaback
authors.forename: G
authors.initials: G
authors.lastname: Leblanc
mesh_terms: D000818:Animals; D001483:Base Sequence; D002417:Cattle; D004247:DNA / Q000235:genetics / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000235:genetics; D015246:Deoxyribonuclease EcoRI / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005696:Galactosidases / Q000235:genetics*; D015971:Gene Expression Regulation, Enzymologic; D005816:Genetic Complementation Test; D026901:Membrane Transport Proteins / Q000235:genetics*; D008715:Methionine; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000502:physiology; D013462:Sulfur Radioisotopes; D027981:Symporters; D014764:Viral Proteins; D000519:alpha-Galactosidase / Q000235:genetics*
chemical_list: D026901:Membrane Transport Proteins; D013462:Sulfur Radioisotopes; D027981:Symporters; D014764:Viral Proteins; D004247:DNA; C021548:melibiose permease; D008715:Methionine; C062210:bacteriophage T7 RNA polymerase; D012321:DNA-Directed RNA Polymerases; D015246:Deoxyribonuclease EcoRI; D005696:Galactosidases; D000519:alpha-Galactosidase