The Mohr-Tranebiaerg-Jensen deafness-dystonia-optic atrophy protein DDP/TIMM8a is translated on cytoplasmic ribosomes but targeted ultimately to the mitochondrial intermembrane space, where it is involved in mitochondrial protein import. STAM I is a cytoplasmic signal-transducing adaptor molecule implicated in cytokine signaling. We report here a direct interaction between DDP and STAM 1, identified by yeast two-hybrid screening and confirmed by co-immunoprecipitation, fusion protein "pull downs," and nuclear redistribution assays. DDP coordinates Zn2+, and Zn2+ was found to stimulate the DDP-STAM1 interaction in vitro. Endogenous STAM1 localizes predominantly to early endosomes, and we found no evidence that STAM1 is imported into mitochondria in vitro. Thus, the DDP-STAM1 interaction likely occurs in the cytoplasm or at the mitochondrial outer membrane. The DDP-STAM1 interaction requires a coiled-coil region in STAM1 that overlaps with the immunoreceptor tyrosine-based activation motif (ITAM), a region previously shown to be important for interaction with Jak2/3 and hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs). Thus, DDP binding may alter the interactions of STAM1 with several cytoplasmic proteins involved in cell signaling and endosomal trafficking. (C) 2003 Elsevier Science (USA). All rights reserved.