Signals for Retention of Cytochrome P450 in the Endoplasmic Reticulum
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According to the current model for the subcellular compartmentalization of proteins, any protein entering the secretory pathway will be transported by bulk flow to the cell surface unless a signal mediating its organelle-specific retention is present. Endoplasmic reticulum (ER) membrane protems, such as cytochromes P450, must have a sequence or structural features that prevent transport from the ER. For some ER membrane proteins, such signals have been identified and are encoded by a short amino acid sequence such as a double lysme motif at the C-terminus of the cytoplasmic tail or positively charged residues at the N-terminus (reviewed in ref. 1 ). ER retention signals may mediate either the direct retention (exclusion from further transport) or retrieval from a post-ER compartment (1 ).
