Like a surgeon stitching up an incision after an operation, cells restore their chromatin after repairing DNA damage. Sarkar et al. identify a protein that helps put the chromatin back in order.
When UV light zaps DNA, the nucleotide excision repair apparatus swings into action, cutting out and replacing the damaged section. Before the work can begin, however, cells must rearrange their chromatin so that the repair enzymes can access the lesion. Scientists haven't determined whether cells remove nucleosomes, push them out of the way, or do both. A further question is how the cells return chromatin structure to normal after repairs are complete. The researchers tested whether the protein Ino80, which helps fix double-stranded DNA breaks, takes part in this process.
Sarkar et al. found that although yeast cells lacking Ino80 were able to mend UV damage, their death rate increased, suggesting a glitch in their post-repair recovery. To find out whether Ino80 helps spur restoration of chromatin structure, the researchers tracked chromatin changes in a gene packed with 14 nucleosomes. After a blast of UV radiation, H3 histones disappeared from the gene almost immediately, the team found. In wild-type cells, the histones returned gradually over the next three hours, matching the pace of DNA repair. But in cells lacking Ino80, the histones hadn't returned after three hours.
The results suggest that Ino80 helps restore nucleosomes after the DNA has been refurbished. A further question to answer, the researchers say, is whether Ino80 also helps patch up DNA damage.