CHOP, also known as GADD153 or DDIT3, is a highly conserved gene in both the structural and regulatory regions. Imposed by unfolded and misfolded proteins, CHOP is significantly induced by ER stress. CHOP is considered a proapoptotic marker of ER stress dependent cell death. CHOP acts as a dominant-negative inhibitor of the transcription factor C/EBP and LAP. It may play an important role in the malignant transformation of nevus to melanoma. The calculated molecular weight of CHOP is 19 kDa, but the protein migrates on an SDS-PAGE gel with an observed molecular mass of 29 kDa (PMID: 1547942).