Protein ZIP code: An informal name for a molecular cell biology system of signals or "address tags" that guide the movement of a protein within a cell. In more technical terms, protein ZIP codes* are molecular signals that direct the protein from the endoplasmic reticulum, where it is assembled, to the cytoplasm of the cell and into other cellular compartments such as the nucleus of the cell.
Mutations in this molecular system of protein "ZIP codes" have been found to cause several human genetic (hereditary) disorders, including cystic fibrosis and hyperoxaluria (a disorder that causes a special type of stone to form in the urine beginning in childhood).
* For the benefit of viewers not familiar with the United States mail system, the term "ZIP code" refers to address codes of the U.S. Postal Service used to sort mail into geographic regions.