FIG. 6.

Models. (A) Hypothetical model for DSB processing by Rad50 complex and Exo1. DSB ends are processed mainly by the Rad50-Rad32 complex. In the absence of Rad50-Rad32 complex, DNA ends can be processed by Exo1, but Ku heterodimer has to be removed from the break site to allow end processing. The Cdc13 function may act through the Exo1 pathway, in parallel to Rad50 (8). (B) Hypothetical model for degradation of C-rich strand at telomere ends in taz1-d cells. Telomere ends in taz1-d cells are processed mainly by the Rad50-Rad32 complex. Because the nuclease domain is not required for this process, we assume that the Rad50 complex recruits an unknown nuclease. In the absence of Rad50 complex, DNA ends can be processed by unknown nucleases, but Ku heterodimer has to be removed from the break site to allow end processing.