title: Genetic and molecular characterization of the Escherichia coli secD operon and its products.
abstract: The secD operon of Escherichia coli is required for the efficient export of proteins. We have characterized this operon, and found that, in addition to secD and secF, it contains the upstream gene yajC, but not the genes queA or tgt, in contrast to previous reports. An analysis of yajC mutations constructed in vitro and recombined onto the chromosome indicates that yajC is neither essential nor a sec gene. The secD operon is not induced in response to either secretion defects or temperature changes. TnphoA fusions have been used to analyze the topology of SecD in the inner membrane; the protein contains six transmembrane stretches and a large periplasmic domain. TnphoA fusions to SecD and SecF have also been recombined onto the chromosome and used to determine the level of these proteins within the cell. Our results indicate that there are fewer than 30 SecD and SecF molecules per cell.
authors.affiliation: Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: K J
authors.initials: KJ
authors.lastname: Pogliano
authors.forename: J
authors.initials: J
authors.lastname: Beckwith
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015870:Gene Expression; D005798:Genes, Bacterial; D006860:Hydrogen Bonding; D008565:Membrane Proteins / Q000235:genetics; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009690:Nucleic Acid Conformation; D015345:Oligonucleotide Probes / Q000737:chemistry; D009876:Operon; D012329:RNA, Bacterial / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D015345:Oligonucleotide Probes; D012329:RNA, Bacterial; D012333:RNA, Messenger; C499394:SecD protein, E coli; C489583:SecF protein, E coli; C075767:secD protein, Bacteria; C075768:secF protein, Bacteria