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The HMGI proteins (HMGI, HMGY and HMGI-C) have an important role in the chromatin organization and interact with different transcriptional factors. The HMGI genes are expressed at very low levels in normal adult tissues, whereas they are very abundant during embryonic development and in several experimental and human tumours. In order to isolate proteins interacting with the HMGI (Y) proteins, a yeast two-hybrid screening was performed using the HMGI (Y) protein as bait. This analysis led to the isolation of homeodomain-interacting protein kinase-2 (HIPK2), a serine/threonine nuclear kinase. HIPK2 co-immunoprecipitates with the HMGI (Y) protein in 293T cells. The interaction between HIPK2 and HMGI (Y) occurs through the PEST domain of HIPK2 and it is direct because in vitro translated HIPK2 binds HMGI (Y). We also show that HIPK2 is able to phosphorylate the HMGI (Y) protein by an in vitro kinase …