title: The translational regulatory function of SecM requires the precise timing of membrane targeting.
abstract: In Escherichia coli, secA expression is regulated at the translational level by an upstream gene (secM) that encodes a presecretory protein. SecM contains a C-terminal sequence motif that induces a transient translation arrest. Inhibition of SecM membrane targeting prolongs the translation arrest and increases SecA synthesis by concomitantly altering the structure of the secM-secA mRNA. Here we show that the SecM signal peptide plays an essential role in this regulatory process by acting as a molecular timer that co-ordinates membrane targeting with the synthesis of the arrest motif. We found that signal peptide mutations that alter targeting kinetics and insertions or deletions that change the distance between the SecM signal peptide and the arrest motif perturb the balance between the onset and release of arrest that is required to regulate SecA synthesis. Furthermore, we found that the strength of the interaction between the ribosome and the SecM arrest motif is calibrated to ensure the release of arrest upon membrane targeting. Our results strongly suggest that several distinctive features of the SecM protein evolved as a consequence of constraints imposed by the ribosome and the Sec machinery.
authors.affiliation: Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Mee-Ngan
authors.initials: MN
authors.lastname: Yap
authors.forename: Harris D
authors.initials: HD
authors.lastname: Bernstein
mesh_terms: D000251:Adenosine Triphosphatases / Q000096:biosynthesis*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000096:biosynthesis*; D002462:Cell Membrane / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D054643:INDEL Mutation; D026901:Membrane Transport Proteins / Q000096:biosynthesis*; D008954:Models, Biological; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D011485:Protein Binding; D014176:Protein Biosynthesis; D021382:Protein Sorting Signals; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D050505:Mutant Proteins; D021382:Protein Sorting Signals; D000069816:SEC Translocation Channels; C497347:SecM protein, E coli; D014157:Transcription Factors; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins