The methyl-directed mismatch repair (MMR) mechanism has been extensively studied 
in vitro and in vivo, but one of the difficulties in determining the biological 
relationships between the MMR-related proteins is the tendency of MutL to 
self-aggregate. The properties of a stable MutL homologue were investigated 
using a thermostable MutL (TmL) from Thermotoga maritima MSB8 and whose size 
exclusion chromatographic and crosslinking analyses were compatible with a 
dimeric form of TmL. TmL underwent conformational changes in the presence of 
nucleotides and single-stranded DNA (ssDNA) with ATP binding not requiring ssDNA 
binding activity of TmL, while ADPnP-stimulated TmL showed a high ssDNA binding 
affinity. Finally, TmL interacted with the T. maritima MutS (TmS), increasing 
the affinity of TmS to mismatched DNA base pairs and suggesting that the role of 
TmL in the formation of a mismatched DNA-TmS complex may be a pivotal 
observation for the study of the initial MMR system. [BMB reports 2009; 42(1): 
53-58].