The DnaJ family comprises a group of chaperone proteins that contain a J domain and have diverse cellular localization and functions. DnaJ proteins play a critical role in the HSP 70 chaperone machine by interacting with HSP 70 to stimulate ATP hydrolysis and are also important mediators of proteolysis and protein degradation. DnaJC1 (DnaJ homolog subfamily C member 1), also designated MTJ1, HTJ1, ERdj1 or DNAJL1, is a 554 amino acid single-pass type I membrane protein found in the membrane of the endoplasmic reticulum, nucleus and microsome. DnaJC1 contains one J domain and two SANT domains, through which it interacts with GRP 78 and AACT, respectively. Via its cytosolic domain, DnaJC1 interacts with ribosomes and likely modulates protein synthesis. The gene encoding DnaJC1 maps to human chromosome 10p12.31 and mouse chromosome 2 A3.