[pre-pro´tēn] a protein precursor that contains a signal peptide sequence; it is a nonpolar sequence at the head of the growing polypeptide chain and is required for its transfer into the cistern of the endoplasmic reticulum; the signal sequence is then cleaved to form the protein or proprotein.
pre·pro·tein
(prē-prō'tēn), A secretory protein with a signal peptide region attached.