Editing Transmembrane domain (section)

=== Membrane recognition factors ===
Once transported, factors assist with insertion of the TMD across the [[Hydrophile|hydrophilic]] layer phosphate "head" group of the [[phospholipid]] membrane.<ref name=":0" /> Quality control factors must be able to discern function and topology, as well as facilitate extraction to the cytosol. The signal recognition particle transports membrane proteins to the Sec [[Translocon|translocation channel]], positioning the ribosome exit tunnel proximal to the [[translocon]] central pore and minimizing exposure of the TMD to cytosol. Insertases can also mediate TMD insertion into the [[lipid bilayer]]. Insertases include the bacterial YidC, mitochondrial Oxa1, and chloroplast Alb3, all of which are [[evolution]]arily related. The [[Conserved sequence|conserved]] [[HRD1|Hrd1]] and [[Derlin-1|Derlin]] enzyme families are examples of membrane bound quality control factors.