Seminar

Structure and interactions of PCNA and ING proteins in DNA replication and chromatin remodeling

Francisco J. Blanco, PhD

Chromosomal DNA replication requires a sliding clamp that encircles the DNA and anchor polymerases preventing their falling off the genomic template. Proliferating Cell Nuclear Antigen is the eukaryotic sliding clamp, with a conserved ring-shaped fold and a central channel larger than the diameter of a DNA double helix. Fast sliding implies weak, transient clamp-DNA interactions. PCNA also interacts with regulatory proteins that arrest the cell cycle progression, like p21, or facilitate the switch from replicative to translesion synthesis polymerases in response to DNA damage, like p15. The intrinsically disorder protein p15 adopts a unique structure when bound to PCNA, and it also binds DNA, suggesting that it may regulate the PCNA sliding velocity on the DNA. Post-translational modifications may further regulate this process, and p15 is found partially diubiquitinated inside the cells. The structural study on the effect of ubiquitination on these interactions is hampered by the difficulties in the preparation of high amounts of ubiquitinated proteins. DNA replication requires the chromatin to be in an accessible open state, which is facilitated by histone acetylation. The INhibitors of Growth tumor suppressor proteins recruit histone modification complexes to the chromatin and are reported to interact with PCNA and other components of the replication machinery. ING proteins dimerize through their N-terminal domain, contain a central disordered region and a C-terminal PlantHomeoDomain. Mutations in the three regions have been described in primary tumors.