Identification by UV resonance Raman spectroscopy of an imino tautomer of 5-hydroxy-2'-deoxycytidine, a powerful base analog transition mutagen with a much higher unfavored tautomer frequency than that of the natural residue 2'-deoxycytidine.
UV resonance Raman spectroscopy was used to detect and estimate the frequency of the unfavored imino tautomer of the transition mutagen 5-hydroxy-2'-deoxycytidine (HO5dCyt) in its anionic form. In DNA, this 2'-deoxycytidine analog arises from the oxidation of 2'-deoxycytidine and induces C --> T transitions with 10(2) greater frequency than such spontaneous transitions. An imino tautomer marker carbonyl band (approximately 1650 cm-1) is enhanced at approximately 65 degrees C against an otherwise stable spectrum of bands associated with the favored amino tautomer. This band is similarly present in the UV resonance Raman spectra of the imino cytidine analogs N3-methylcytidine at high pH and N4-methoxy-2'-deoxycytidine at pH 7 and displays features attributable to the imino form of C residues and their derivatives. The fact that the imino tautomer of HO5dCyt occurs at a frequency consistent with its high mutagenic enhancement lends strong support to the hypothesis that unfavored base tautomers play important roles in the mispair intermediates of replication leading to substitution mutations.
Suen
W
W
Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
Spiro
T G
TG
Sowers
L C
LC
Fresco
J R
JR
D004247:DNA / Q000737:chemistry; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007097:Imines / Q000032:analysis / Q000737:chemistry; D009153:Mutagens / Q000032:analysis* / Q000737:chemistry; D012997:Solvents; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D013059:Spectrum Analysis, Raman / Q000379:methods; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D007097:Imines; D009153:Mutagens; D012997:Solvents; D003841:Deoxycytidine; C074071:5-hydroxy-2'-deoxycytidine; D004247:DNA