MutL_Trans: transducer domain, having a ribosomal S5 domain 2-like fold, conserved in the C-terminal domain of type II DNA topoisomerases (Topo II) and DNA mismatch repair (MutL/MLH1/PMS2) proteins. This transducer domain is homologous to the second domain of the DNA gyrase B subunit, which is known to be important in nucleotide hydrolysis and the transduction of structural signals from ATP-binding site to the DNA breakage/reunion regions of the enzymes. The GyrB dimerizes in response to ATP binding, and is homologous to the N-terminal half of eukaryotic Topo II and the ATPase fragment of MutL. Type II DNA topoisomerases catalyze the ATP-dependent transport of one DNA duplex through another, in the process generating transient double strand breaks via covalent attachments to both DNA strands at the 5' positions. Included in this group are proteins similar to human MLH1 and PMS2. MLH1 forms a heterodimer with PMS2 which functions in meiosis and in DNA mismatch repair (MMR). Cells lacking either hMLH1 or hPMS2 have a strong mutator phenotype and display microsatellite instability (MSI). Mutation in hMLH1 accounts for a large fraction of Lynch syndrome (HNPCC) families.