Stability of 2'-deoxyxanthosine in DNA.
The deamination of nucleobases in DNA occurs by a variety of mechanisms and results in the formation of hypoxanthine from adenine, uracil from cytosine, and xanthine and oxanine from guanine. 2'-Deoxyxanthosine (dX) has been assumed to be an unstable lesion in cells, yet no study has been performed under biological conditions. We now report that dX is a relatively stable lesion at pH 7, 37 degrees C and 110 mM ionic strength, with a half-life (t(1/2)) of 2.4 years in double-stranded DNA. The stability of dX as a 2'-deoxynucleoside (t(1/2) = 3.7 min at pH 2; 1104 h at pH 6) was increased substantially upon incorporation into a single-stranded oligodeoxynucleotide, in which the half-life of dX at different pH values was found to range from 7.7 h at pH 2 to 17 700 h at pH 7. Incorporation of dX into a double-stranded oligodeoxynucleotide resulted in a statistically insignificant increase in the half-life to 20 900 h at pH 7. Data for the pH dependence of the stability of dX in single-stranded DNA were used to determine the rate constants for the acid-catalyzed (2.6 x 10(-5) x s(-1)) and pH-independent (1.4 x 10(-8) x s(-1)) depurination reactions for dX as well as the dissociation constant for the N7 position of dX (6.1 x 10(-4) M). We conclude that dX is a relatively stable lesion that could play a role in deamination-induced mutagenesis.
Vongchampa
Viengsai
V
Biological Engineering Division, 56-787, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Dong
Min
M
Gingipalli
Lakshman
L
Dedon
Peter
P
D000586:Amination; D004247:DNA / Q000737:chemistry*; D003853:Deoxyribonucleosides / Q000737:chemistry* / Q000378:metabolism; D006207:Half-Life; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D009838:Oligodeoxyribonucleotides / Q000737:chemistry
D003853:Deoxyribonucleosides; D009838:Oligodeoxyribonucleotides; C077801:2'-deoxyxanthosine; D004247:DNA