On the basis of telomere lengths of mutant combinations of various checkpoint related proteins ( Rad 1 , Rad 3 , Rad 9 , Rad 17 , Rad 26 , Hus 1 , Crb 2 , Chk 1 , Cds 1 ) , Tel 1 , a telomere binding protein ( Taz 1 ) , and DNA repair proteins ( Ku 70 , Rad 32 ) , we conclude that Rad3 / Rad26 and Tel1 / Rad32 represent two pathways required to maintain telomeres and prevent chromosome circularization . ^^^