A Novel GT-Mismatch Binding Protein That Recognizes Strict DNA Sequences with High Affinity

Mismatched or damaged base pairs in DNA are mutagenic and both eukaryotes and prokaryotes have a series of repair systems that decrease a spontaneous mutation rate. All exocyclic amino groups of cytosine(C), adenine(A), and guanine(G) contribute to hydrogen bonds for base pairing. High temperature and oxidative stresses increase the deamination of these bases and methylated C. These deaminated sites would be initially recognized by components of DNA repair system. We discovered a novel G/thymine(T)-mismatch binding protein (nGTBP) that bound, with high affinity, to a minimal 14-mer DNA heteroduplex with a strict 5'-TRT GNB-3' sequence (R for purine, N for any bases, and B for "not A," namely for C, G, or T ). This italicized G position mismatched with T could be replaced by hypoxanthine, the deaminated A. The nGTBP, however, barely recognized DNA duplexes individually containing 8-oxo-G, thymine glycol, and 5-methylcytosine.