Abstract
Programmed DNA double-strand breaks (DSBs) are required for meiotic recombination, but the number is strictly controlled because they are potentially harmful. Here we report a novel protein, Pars11, which is required for Spo11-dependent DSB formation in the protist Tetrahymena. Pars11 localizes to chromatin early in meiotic prophase in a Spo11-independent manner and is removed before the end of prophase. Pars11 removal depends on DSB formation and ATR-dependent phosphorylation. In the absence of the DNA damage sensor kinase ATR, Pars11 is retained on chromatin and excess DSBs are generated. Similar levels of Pars11 persistence and DSB overproduction occur in a non-phosphorylatable pars11 mutant. We conclude that Pars11 supports DSB formation by Spo11 until enough DSBs are formed; thereafter, DSB production stops in response to ATR-dependent degradation of Pars11 or its removal from chromatin. A similar DSB control mechanism involving a Rec114-Tel1/ATM-dependent negative feedback loop regulates DSB formation in budding yeast. However, there is no detectable sequence homology between Pars11 and Rec114, and DSB numbers are more tightly controlled by Pars11 than by Rec114. The discovery of this mechanism for DSB regulation in the evolutionarily distant protist and fungal lineages suggests that it is conserved across eukaryotes.