Gs. Schuerman et al., A THYMINE-LIKE BASE ANALOG FORMS WOBBLE PAIRS WITH ADENINE IN A Z-DNADUPLEX, Journal of Molecular Biology, 282(5), 1998, pp. 1005-1011
The DNA hexamer d(CACGPG), in which dP is the ambivalent pyrimidine nu
cleoside analogue H,8H-3,4-dihydropyrimido[4,5-c][1,2]oxazin-7-one), c
rystallises as a left-handed Z-DNA duplex. X-ray analysis at 1.5 Angst
rom shows that both PA base-pairs are of the wobble type. This result
appears inconsistent with other evidence from hybridisation and NMR st
udies of P-containing oligonucleotides, which suggests that, while P c
an form stable base-pairs with either A or G, thymine-like properties
are more pronounced. Thermal denaturation experiments over a range of
solution pH values indicate that protonation of the P A base-pairs is
unlikely to be responsible for the anomalous behaviour. No specific cr
ystal packing effects can be identfied as an explanation and it is con
cluded that base stacking and other interactions between nucleotide re
sidues in Z-DNA are responsible. (C) 1998 Academic Press.