GCIP, a newly identified cyclin D-interacting protein, was found to reduce the phosphorylation of retinoblastoma protein and inhibit E2F1-mediated transcriptional activity. To explore more GCIP interacting proteins, the yeast two-hybrid screening using GCIP as st bait protein was performed. One novel gene, p29, was demonstrated to associate with GCIP in the yeast two-hybrid method and in vitro GST pull-down assay. Multiple tissue Northern blot analysis showed. that p29 was abundantly expressed in the heart, skeletal muscle, and kidney relative to other tissues. The transient expression of HA-tagged p29 in HeLa cells localized in the nucleus. Taken together, we have isolated a novel protein, p29, which may be involved in the functional regulation of GCIP.