The Nucleosome Binding Protein HMGN1 Interacts with PCNA and Facilitates Its Binding to Chromatin

Abstract

Proliferating cell nuclear antigen (PCNA) is a ubiquitous protein that interacts with multiple partners and regulates nuclear activities, including chromatin assembly, histone modifications, replication, and DNA damage repair. The role of specific partners in regulating PCNA activities is not fully understood. Here we identify the nucleosome binding protein HMGN1 as a new PCNA-interacting protein that enhances the binding of PCNA to chromatin but not to purified DNA. Two tetrapeptides in the conservative domain of HMGN1 contain amino acids necessary for the binding of HMGN1 to PCNA. Deletion of both tetrapeptides abolishes the HMGN1-PCNA interaction. PCNA preferentially binds to the linker DNA adjacent to an HMGN-containing nucleosome. In living cells, loss of HMGN1 decreases the rate of PCNA recruitment to damaged DNA sites. Our study identifies a new factor that facilitates the interaction of PCNA with chromatin and provides insights into mechanisms whereby nucleosome binding architectural proteins affect the cellular phenotype.

ACKNOWLEDGMENTS

We thank T. Veenstra (Laboratory of Proteomics and Analytical Technologies, NCI—Frederick) for MS analysis, S. Garfield (Confocal Core Facility, LEC, NCI) for help with imaging experiments, and S. Khan and K. Kraemer (CCR, NCI) for help with irradiation experiments and discussions.

This project was supported by the Center for Cancer Research, intramural program of the NCI, NIH, by contract number N01-CO-12400 granted by NCI, NIH, and by a JSPS research fellowship from the Japanese Biomedical and Behavioral Research at NIH to T.K. The yeast RFC and human RFC preparations were generous gifts from Paul Modrich (Duke University).