Nucleic Acids Research, 1985, Vol. 13, No. 16 5949-5963
© 1985
Articles |
UV irradiation of nucleic acids: formation, purification and solution conformational analysis of the ‘6-4 lesion’ of dTpdT
Biophysics Department, Roswell Park Memorial Institute Buffalo, NY 14263, USA
*To whom correspondence should be addressed
Received April 18, 1985. Revised July 19, 1985. Accepted July 19, 1985.
Irradiation of dTpdT with 300 kJ/m2 of 254 nm produces numerous photoproducts, one of which labeled dT6pd4T[l] was purified by HPLC. dT6pd4T has a UV spectrum (H2O, pH 7) with 
max = 326 nm and min = 265 nm, and a P-31 NMR resonance at -3.46 ppm (normal dTpdT occurs at -4.01 ppm; TMP, 30°C). 2-D COSY NMR spectra facilitated proton resonance assignments and 2-D NOESY spectra aided analysis of spatial orientation. Carbon-13 and proton-coupled P-31 NMR spectra of dT6pd4T were also obtained. These analyses indicate: (1) C5=C6 of dT6p- is saturated and the -pd4T base 1s more aromatic; (2) the dT6p- base possesses a configuration of 5R, 6S; (3) dT6p- and -pd4T have anti-type glycosidic conformations; (4) furanose conformation of dT6p- is mainly C3'-endo and that of -pd4T exists in a C3'-endo 
C3'-exo; (5) exocyclic bonds 
(C5'-C4'), ß(05'-C5') and 
(C3'-03') are non-classical rotamers; (6) dihedral angle about (C3'-03') is smaller relative to dTpdT.