A ribosome-nascent chain sensor of membrane protein biogenesis in Bacillus subtilis.
Proteins in the YidC/Oxa1/Alb3 family have essential functions in membrane protein insertion and folding. Bacillus subtilis encodes two YidC homologs, one that is constitutively expressed (spoIIIJ/yidC1) and a second (yqjG/yidC2) that is induced in spoIIIJ mutants. Regulated induction of yidC2 allows B. subtilis to maintain capacity of the membrane protein insertion pathway. We here show that a gene located upstream of yidC2 (mifM/yqzJ) serves as a sensor of SpoIIIJ activity that regulates yidC2 translation. Decreased SpoIIIJ levels or deletion of the MifM transmembrane domain arrests mifM translation and unfolds an mRNA hairpin that otherwise blocks initiation of yidC2 translation. This regulated translational arrest and yidC2 induction require a specific interaction between the MifM C-terminus and the ribosomal polypeptide exit tunnel. MifM therefore acts as a ribosome-nascent chain complex rather than as a fully synthesized protein. B. subtilis MifM and the previously described secretion monitor SecM in Escherichia coli thereby provide examples of the parallel evolution of two regulatory nascent chains that monitor different protein export pathways by a shared molecular mechanism.
Division of Biological Sciences, University of California, San Diego, CA, USA.
Shinobu
S
Chiba
Anne
A
Lamsa
Kit
K
Pogliano
D001412:Bacillus subtilis / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D015964:Gene Expression Regulation, Bacterial; D008565:Membrane Proteins / Q000096:biosynthesis*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis / Q000235:genetics / Q000502:physiology*; D012270:Ribosomes / Q000378:metabolism*; D015854:Up-Regulation
D001426:Bacterial Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C030069:spore-specific proteins, Bacillus