Structural biology of protein-protein interactions involved in DNA replication under DNA damage

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DNA clamp is involved in various cellular events on DNA including DNA replication, repair and replication, and functions as a scaffold protein in those events. DNA clamp forms a ring-shaped trimer that encircles the DNA double helix and slides freely along the DNA axis. PCNA and RAD9/HUS1/RAD1(9-1-1) are DNA clamp in eukaryote. PCNA is a homo-trimer, whereas 9-1-1 is a hetero-trimer. Each subunit of 9-1-1 is composed of PCNA-like domain. However, RAD9 has an additional domain with a molecular weight of 13 kD in the C-terminus. Structure of 9-1-1 trimer of PCNA-like domains is similar to that of PCNA trimer. In this study, we prepared the C-terminal domain of RAD9CTD and performed structural analysis by small angle X-ray scattering(SAXS). Some archaea have heterotrimeric DNA clamp(PCNA1-PCNA2-PCNA3). We reveals that PCNA2-PCNA3 from Sulfolobus tokodaii forms tetrameric ring structure in solution by SAXS.