Is my DNA fixed yet?

A broken chromosome (a double-strand DNA break) activates the DNA damage checkpoint to prevent cells from carrying out mitosis until the break has been repaired.  Repair of the break involves the modification and the removal of histone protein octamers from DNA around the break and these must be reestablished when repair is complete.  In a new paper in PNAS, Brandeis alumnus Jung-Ae Kim (Ph.D., Molecular and Cell Biology, 2008) and Professor James Haber show that when two of the major histone chaperone protein complexes (Asf1 and CAF-1) are deleted in yeast cells, their absence prevents cells from turning off the DNA damage checkpoint and hence cells stay permanently arrested.   These results suggest that cells specifically monitor the re-establishment of normal chromatin status after DNA repair.