FIG. 8.

Schematic representation of Mre11, Rad50, and Xrs2 (Nbs1). The phosphodiesterase motifs of Mre11 are labeled MI through MIV, and DNA binding sites are labeled DB site A and B. The Mre11-D16A, Mre11-D56N, Mre11-H125N, Mre11-H213Y, and Mre11-6 mutants are nuclease defective in vitro. Residue Pro84 is mutated in the mre11-S allele, and Pro162 is mutated in the mre11-1 temperature-sensitive allele. The mre11-N113S and mre11-Q623Z alleles correspond to the mutations in the A-TLD patients. Rad50 contains two coiled-coil domains separating the Walker A and B motifs for NTP binding and hydrolysis. The hook domain, containing the conserved CXXC motif, is located between the two coiled-coil domains. The positions of the rad50S alleles, rad50-R20M and rad50-K81I, are shown.