DNA binding and protein-protein interaction sites in MutS, a mismatched DNA recognition protein from Thermus thermophilus HB8

The mismatch repair system repairs mismatched base pairs, which are caused by either DNA replication errors, DNA damage, or genetic recombination. Mismatch repair begins with the recognition of mismatched base pairs in DNA by MutS. Protein denaturation and limited proteolysis experiments suggest that Thermus thermophilus MutS can be divided into three structural domains as follows: A (N-terminal domain), B (central domain), and C (C-terminal domain) (Tachiki, H., Kato, R., Masui, R., Hasegawa, K., Itakura, H., Fukuyama, K., and Kuramitsu, S. (1998) Nucleic Acids Res. 26, 4153-4159). To investigate the functions of each domain in detail, truncated genes corresponding to the domains were designed. The gene products were overproduced in Escherichia coli, purified, and assayed for various activities. The MutS-MutS protein interaction site was determined by size-exclusion chromatography to be located in the B domain. The B domain was also found to possess nonspecific double-stranded DNA-binding ability. The C domain, which contains a Walker's A-type nucleotide-binding motif, demonstrated ATPase activity and specific DNA recognition of mismatched base pairs. These ATPase and specific DNA binding activities were found to be dependent upon C domain dimerization.