DNA MODIFICATIONS BY THE MUTAGEN GLYOXAL - ADDUCTION TO G AND C, DEAMINATION OF C AND GC AND GA CROSS-LINKING

The mutagen glyoxal was reacted with DNA or deoxynucleosides under phy siological conditions (pH 7.4, 37 degrees C) in vitro and the products were analyzed by HPLC coupled with a photodiode array UV detector. Th e efficient formation of a cyclic glyoxal-dG adduct (dG(+)) was observ ed in DNA, as well as with dG. The monomeric dG(+) was gradually decom posed to dG at pH 7.4 and 37 degrees C (t(1/2) 14.8 h). However, the d G(+) formed in single- and double-stranded DNA was rather stable under physiological conditions and the half-lives were 19 and 40 times long er respectively than that of the monomer (t(1/2) 285 and 595 h respect ively). By reaction of glyoxal with deoxycytidine (dC), the deaminatio n products deoxyuridine and 5-hydroxyacetyl-dC (dC(+)) were formed. Un der the same conditions, 5-methyl-dC was deaminated to dT at a higher rate. Deoxyuridine was also formed in DNA by glyoxal treatment. When g lyoxal was reacted with various combinations of deoxynucleosides for a prolonged period, dG-glyoxal-dC (GgC), dG-glyoxal-dA (GgA), dG-glyoxa l-dG (GgG) and dC-glyoxal-dC (CgC) cross-links were detected, although structures were not assigned unequivocally. Among these, the former t wo, the GC and GA cross-links, were detected in glyoxal-treated DNA, T he yields of these products in DNA were in the following order; dG(+) > dU > GgA > GgC > dC+, These DNA modifications may be relevant to gly oxal-induced mutations at GC pairs.