Cell Cycle Dependent Binding of HMGN1/2 Proteins to Chromatin

The high mobility group nuclear proteins 1/2 (HMGN1/2) specifically bind to nucleosomal core particles and are known to have a critical role in transcription, replication, DNA repair, and carcinogenesis. Previous reports based on immunofluorescence and live cell imaging yielded controversial results related to the binding properties of HMGN proteins to the mitotic chromatin. In the present work, we have studied the binding properties of HMGN proteins to the chromatin during cell cycle. Using immunofluorescence microscopy, we have shown that the endogenous HMGN1/2 proteins co‐localize with the interphase but not with mitotic chromatin. Nulceosomal mobility shift assays with wild type and glutamic acid mutations in the nucleosomal binding domain of HMGN1 demonstrate that the wild type but not the mutant HMGN1 bind to the core particles. Where as, in live cells, both wild type and mutant proteins appear to be associated with the mitotic chromatin. Bimolecular complementation assays showed that HMGN proteins generate fluorescence complementation in interphase but not in mitotic nuclei. In addition, results from biochemical assays further confirmed the altered binding properties of HMGN proteins between interphase and mitotic chromatin. To this end, our studies demonstrate the dynamic nature of HMGNs interaction with the chromatin during various stages of cell cycle.