Two fundamentally distinct PCNA interaction peptides contribute to chromatin assembly factor 1 function

Area of Science:

• Molecular Biology
• Cell Biology
• Epigenetics

Background:

• Chromatin assembly factor 1 (CAF-1) deposits histones H3-H4 behind replication forks.
• CAF-1 interacts with proliferating cell nuclear antigen (PCNA), a key replication factor.
• Mechanisms for harmonious function of PCNA-binding proteins at replication forks are unclear.

Purpose of the Study:

• Investigate the distinct roles of two PCNA interaction peptides (PIPs) in human CAF-1 (p150).
• Determine how these PIPs contribute to nucleosome assembly and targeting to replication sites.
• Elucidate the mechanism enabling CAF-1 function without interfering with other PCNA-mediated processes.

Main Methods:

• In vitro binding assays to assess PCNA interaction strength of p150 PIPs.
• In vivo studies to evaluate the role of PIPs in nucleosome assembly and targeting to replication foci.
• Comparative analysis of p150 PIPs with canonical PIPs (e.g., p21).

Main Results:

• The N-terminal PIP binds strongly to PCNA but is dispensable for nucleosome assembly.
• The internal PIP (PIP2), despite weak PCNA binding, is essential for nucleosome assembly and p150 targeting.
• p150 PIPs preferentially inhibit nucleosome assembly, not DNA synthesis, unlike canonical PIPs.

Conclusions:

• Human CAF-1 p150 possesses two distinct PIPs with differential roles in PCNA interaction and function.
• PIP2 is critical for CAF-1's role in DNA replication-coupled nucleosome assembly.
• CAF-1's unique PIP features facilitate its function at replication forks without disrupting essential DNA replication processes.