FOXK2 transcription factor is a novel G/T-mismatch DNA binding protein.

DNA mismatch repair is an important mechanism in the prevention of mutations. We reported the existence in the HL60 cell line of a novel G/T-mismatch DNA-binding protein (nGTBP) requiring strict DNA sequences. In this report, we identify the FOXK2 transcription factor as the nGTBP. FOXK2 fragments were obtained as the only clones with specifically binding activity to the G/T-mismatch DNA by screening of a human brain expression library. The recombinant forkhead domain of FOXK2 specifically recognized the G/T-mismatch DNA. The forkhead domain also recognized hypoxanthine/T and G/uracil, derived from the deamination of the exocyclic amino groups of A/T and G/C, respectively. An electrophoretic mobility shift assay (EMSA) analysis using HL60 cell nuclear extract and antibody raised against FOXK2 resulted in the exclusive binding of FOXK2 to G/T-mismatch DNA. Furthermore, FOXK2 bound to G/T-mismatch DNA with higher affinity than 'match' FOXK2 consensus DNA. We therefore propose that FOXK2 is a G/T-mismatch DNA-binding protein and a deaminated DNA-binding protein.