Down syndrome (DS) is caused by trisomy for human chromosome 21 and is the most common genetic cause of mental retardation. The distal 10 Mb region of the long arm of the chromosome has been proposed to be associated with many of the abnormalities seen in DS. This region is often referred to as the Down syndrome critical region (DSCR). We report here the results of our analyses of the DSCR protein 2 (DSCR2). Results from transiently transfected COS-1 and HEK293 cells suggest that DSCR2 is synthesized as a 43 kDa precursor protein, from which the N-terminus is cleaved resulting in a polypeptide of 41 kDa. The polypeptide is modified by still uncharacterized co- or post-translational modifications increasing the predicted molecular weight of 32.8 kDa by about 10 kDa. Analyses of the only putative N-glycosylation site by in vitro mutagenesis excluded the possibility of the contribution of N-glycosylation to this increase in molecular weight. Further, the results of intracellular localization studies and membrane fractionation assays indicate that DSCR2 is targeted to a cytoplasmic compartment as a soluble form. (C) 2004 Published by Elsevier Inc.