JM4 (Jena-Muenchen 4), also known as PRAF2 (PRA1 domain family, member 2), is a 178 amino acid endosomal multi-pass membrane protein involved in vesicular trafficking and Endoplasmic reticulum/Golgi transport. As a member of the PRA1 family, JM4 contains four putative transmembrane (TM) domains, interacts with the CC chemokine receptor 5 (CCR5) and colocalizes with Calnexin in the ER and mannose 6-phosphate receptor (CD-MPR) in the Golgi apparatus.