Architecture of high mobility group protein I-C center dot DNA complex andits perturbation upon phosphorylation by Cdc2 kinase

The high mobility group I-C (HMGI-C) protein is an abundant component of ra pidly proliferating undifferentiated cells. High level expression of this p rotein is characteristic for early embryonic tissue and diverse tumors. HMG I-C can function as an architectural factor enhancing the activity of trans cription factor NF-kappa B on the beta-interferon promoter. The protein has three minor groove DNA-binding domains (AT-hooks), Here, we describe the c omplex of HMGI-C with a fragment of the beta-interferon promoter, We show t hat the protein binds to NRDI and PRDII elements of the promoter with its f irst and second AT-hook, respectively. Phosphorylation by Cdc2 kinase leads to a partial derailing of the AT-hooks from the minor groove, affecting ma inly the second binding domain. In contrast, binding to long AT stretches o f DNA involves contacts with all three AT-hooks and is marginally sensitive to phosphorylation, Our data stress the importance of conformation of the DNA binding site and protein phosphorylation for its function.