DISTINCT ROLES OF 2 SEPARABLE IN-VITRO ACTIVITIES OF YEAST MRE11 IN MITOTIC AND MEIOTIC RECOMBINATION

In Saccharomyces cerevisiae, Mre11 protein is involved in both double- strand DNA break (DSB) repair and meiotic DSB formation. Here, we repo rt the correlation of nuclease and DNA-binding activities of Mre11 wit h its functions in DNA repair and meiotic DSB formation, Purified Mre1 1 bound to DNA efficiently and was shown to have Mn2+-dependent nuclea se activities, A point mutation in the N-terminal phosphoesterase moti f (Mre11D16A) resulted in the abolition of nuclease activities but had no significant effect on DNA binding. The wild-type level of nuclease activity was detected in a C-terminal truncated protein (Mre11 Delta C49), although it had reduced DNA-binding activity, Phenotypes of the corresponding mutations were also analyzed. The mre11D16A mutation con ferred methyl methanesulfonate-sensitivity to mitotic cells and caused the accumulation of unprocessed meiotic DSBs. The mre11 Delta C49 mut ant exhibited almost wild-type phenotypes in mitosis, However, in meio sis, no DSB formation could be detected and an aberrant chromatin conf iguration was observed at DSB sites in the mre11 Delta C49 mutant. The se results indicate that Mre11 has two separable functional domains: t he N-terminal nuclease domain required for DSB repair, and the C-termi nal dsDNA-binding domain essential to its meiotic functions such as ch romatin modification and DSB formation.