gammaH2A binds Brc1 to maintain genome integrity during S-phase

Area of Science:

• Cellular Biology
• Molecular Biology
• Genetics

Background:

• ATM and ATR kinases phosphorylate histone H2AX (gammaH2AX) at DNA damage sites, recruiting repair proteins.
• Proteins binding gammaH2AX at double-strand breaks (DSBs) are known, but not those involved in replication stress responses.

Purpose of the Study:

• To investigate the role of the fission yeast protein Brc1 in DNA damage response, particularly during replication stress.
• To characterize the interaction between Brc1 and gammaH2A and its functional significance.

Main Methods:

• Genetic analysis
• Biochemical assays
• Small angle X-ray scattering (SAXS)
• X-ray crystallography

Main Results:

• Brc1 binds to gammaH2A, forming nuclear foci that are both spontaneous and DNA damage-induced.
• Spontaneous Brc1 foci localize to ribosomal DNA repeats, associated with genomic instability.
• DNA damage-induced Brc1 foci colocalize with DSB response factors.
• gammaH2A binding is essential for Brc1 function.
• X-ray crystallography revealed how Brc1's BRCT domains bind gammaH2A and identified a DNA-mimicking surface on Brc1.

Conclusions:

• Brc1 is a key protein in the chromatin-specific response to replication-associated DNA damage.
• The interaction between Brc1 and gammaH2A is critical for Brc1's function in DNA repair.
• Structural studies provide insights into the molecular mechanisms of Brc1-gammaH2A binding specificity.