Structure of d(TGCGCA)₂ at 293 K: comparison of the effects of sequence and temperature

The crystal structure of a hexameric DNA fragment with the sequence d(TGCGCA)₂ has been solved and refined at 293 K at a resolution of 1.64 Å. The molecule adopts a left-handed Z-type helical conformation which is common in alternating pyrimidine-purine sequences. The presence of A·T base pairs at the two terminals does not perturb the structure to any great degree. However, several sequence-specific microstructural changes are noticeable. The structure of the identical sequence determined at 120 K involving somewhat different crystallization conditions has been reported previously [Harper et al. (1998), Acta Cryst. D54, 1273-1284]. A comparison of the present structure with that at low temperature and with that of d(CGCGCG)₂ shows that the effect of the change in sequence is greater than the combined effect of changes in temperature and environment.