Identification of a SecM segment required for export-coupled release from elongation arrest.

SecM in Escherichia coli has two functionally crucial regions. The arrest motif near the C-terminus interacts with the ribosomal exit tunnel to arrest its own translational elongation. The signal sequence at the N-terminus directs the SecM nascent polypeptide to the Sec-mediated export pathway to release the arrested state of translation. Here, we addressed the importance of the central region of SecM. Characterization of internal substitution and deletion mutants revealed that a segment from residue 100 to residue 109 is required for the export-coupled release of the SecM nascent chain from the elongation-arrested state. Thus, the central region of SecM is not just a geometric linker but it participates actively in the regulation of translation arrest.