 Human chromosomal translocation t(12;21)(p12;q22) is one of the most frequent rearrangement in human leukemia, and produces the TEL/RUNX1 fusion protein.     ///    It appears that loss of TEL function activates a pathway that cooperates with TEL/RUNX1 and sequesters coactivator(s) into nonfunctional complex in the cytoplasm thus inhibiting transcription of target genes..     ///    Immunoprecipitation and immunofluorescence analysis showed that p300 interacts with TEL/RUNX1 and is sequestered in the cytoplasm by it.     ///    These results suggest that the p300-TEL/RUNX1 complex and heterodimerization of TEL/RUNX1 with TEL may be responsible for the ability of TEL/RUNX1 to inhibit RUNX1-mediated transactivation.     ///    "Here, we demonstrate that the repressor activity of TEL/ RUNX1 differs from that of TEL, even though both TEL and TEL/RUNX1 interact with the nuclear hormone co-repressor (N-CoR) and histone deacetylase (mSin3A) in vivo. "    ///    "Co-immunoprecipitation experiments demonstrated that TEL/RUNX1 forms homodimers in vivo, and heterodimerizes with the TEL when the two proteins are expressed together. "    ///    The TEL/RUNX1 fusion protein creates a transcriptional repressor that interferes in dominant fashion with RUNX1-dependent transactivation.     ///    Mechanism of transcriptional repression by TEL/RUNX1 fusion protein.. 