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Docking protein --> signal recognition particle receptor

receptor for the signal recognition particle (SRP) found in the membrane of the endoplasmic reticulum. Also called docking protein. Heterodimeric, both protomers having gtp binding capacity, though dissimilar binding sites. Not until the complex of SRP, ribosome, message and nascent polypeptide Chain binds to the SRP receptor is the block to further chain elongation released and concurrently the SRP is released, leaving the ribosome attached to the endoplasmic reticulum membrane. Cotranslational transport of the polypeptide delivers it into the lumen of the er.