I heard that transmembrane domains (TMDs) can also serve the purpose of signal peptide (SP). Can somebody provide me literature with that? I generated a transmembrane protein that lacks a portion in the N-terminal. So this truncated protein does not have the signal peptide (SP), but it functions just like the full length protein. This indicate that the truncated protein is localized to the correct place (cytoplasmic membrane) for its function. However, people criticize that the truncated protein can not go to cytoplasmic membrane without the SP. Tagged protein can not definitively tell whether the truncated protein is localized to the membrane.