Sensor protein that up-regulates translation of the secondary membrane protein insertase (MisCB/YqjG) when activity of the primary membrane protein insertase (MisCA/SpoIIIJ) is limited. Acts as a ribosome-nascent chain complex. When the primary membrane protein insertase activity or level is reduced, the membrane insertion of MifM is impaired, which induces arrest of MifM translation and unfolding of the mRNA hairpin. Unfolding leads to translation of the downstream gene, which encodes the secondary membrane protein insertase MisCB/YqjG. Translation arrest of MifM is mediated by interaction of its C-terminal domain with the ribosomal polypeptide exit tunnel. Undergoes multisite stalling, which may allow a sufficient duration of ribosomal stalling and consequently sufficient levels of MisCB/YqjG