As a model to investigate the biological and biochemical functions of cyclin D1-Cdk2 complexes, and the mechanisms by which cyclin D1 activates Cdk2, a cyclin D1-Cdk2 fusion gene was constructed.     ///    "Furthermore, cyclin D1-Cdk2 complexes catalyze Rb phosphorylation on multiple sites in vitro. "    ///    "This report demonstrates that Cdk2 in cyclin D1-Cdk2 complexes from mammary epithelial cells is phosphorylated on the activating phosphorylation site, Thr(160). "    ///    "Cyclin D1-Cdk2 complexes were previously observed in human breast cancer cell lines, but their role in cell cycle regulation and transformation was not investigated. "    ///    We propose that cyclin D1-Cdk2 complexes mediate some of the transforming effects of cyclin D1 and demonstrate that the cyclin D1-Cdk2 fusion protein is a useful model to investigate the biological functions of cyclin D1-Cdk2 complexes..     ///    Construction of a cyclin D1-Cdk2 fusion protein to model the biological functions of cyclin D1-Cdk2 complexes..     ///    The cyclin D1-Cdk2 fusion protein expressed in epithelial cells was phosphorylated on Thr(160) and catalyzed the phosphorylation of Rb on multiple sites in vitro and in vivo.     ///    "Cells stably expressing the cyclin D1-Cdk2 fusion protein exhibited several hallmarks of transformation including hyperphosphorylation of Rb, resistance to TGFbeta-induced growth arrest, and anchorage-independent proliferation in soft agar. "