Signal anchors are important in the topogenesis of membrane proteins. Some are non-cleavable, and so remain attached to the protein after its insertion. Reverse signal anchors allow the insertion of multi-pass membrane proteins, controlling how the protein is inserted.
With single-pass membrane proteins, the translocator recognises a stop transfer sequence, causing it to dissociate from the membrane protein to allow the protein’s insertion.
Where a protein has two of more transmembrane domains, start transfer sequences are also used. These allow sideways release of the protein into the membrane, and leaving the N and C termini on the same side.
Generally, positively charged residues are found intracellularly, as described by the positive inside rule. This is used to determine the protein orientation, allowing the N or C terminus to be favoured with both single and multi-pass membrane proteins.