The structural maintenance of chromosome 3 protein (SMC3) is a component of the multimeric cohesin complex that holds sister chromatids together and prevents their premature separation during mitosis. By screening a human cDNA library for interacting proteins we have established that the proto-oncogene RET finger protein (RFP) interacts with SMC3. The sites of interaction map to part of the central coiled coil region of RFP and to the C-terminal region of the SMC3 globular hinge domain. SMC3/RFP interaction was confirmed in vivo by co-immunoprecipitation studies and by performing mammalian two-hybrid interaction assays. Cytoimmunolocalization experiments showed that SMC3 and RFP co-localize in the same cell substructures. Overexpression of RFP in NIH3T3 cells significantly increased the fraction of SMC3 recovered in the nucleus supporting the idea that RFP regulates the intracellular distribution of SMC3. These studies identify a novel SMC3-interacting protein that may affect SMC3 availability to complex with its cohesin partners. (c) 2005 Elsevier Inc. All rights reserved.