KKXX and for some proteins XKXX is a target peptide motif located in the C terminus in the amino acid structure of a protein responsible for retrieval of endoplasmic reticulum (ER) membrane proteins  from the Golgi apparatus. The signal interacts with the COPI protein complex to target the ER from the cis end of the Golgi apparatus by retrograde transport. See also ER retention KDEL (amino acid sequence) 
KKXX and for some proteins XKXX is a target peptide motif located in the C terminus in the amino acid structure of a protein responsible for retrieval of endoplasmic reticulum (ER) membrane proteins to and from the Golgi apparatus. These ER membrane proteins are transmembrane proteins that are then embedded into the ER membrane after transport from the Golgi. This motif is exclusively cytoplasmic and interacts with the COPI protein complex to target the ER from the cis end of the Golgi apparatus by retrograde transport. See also ER retention KDEL (amino acid sequence) COPI Signal peptide Protein targeting
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to and
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The signal
These ER membrane proteins are transmembrane proteins that are then embedded into the ER membrane after transport from the Golgi. This motif is exclusively cytoplasmic and
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COPI Signal peptide Protein targeting