T. D. Sakore, H. M. Sobell, F. Mazza
Aug 14, 1969
Citations
0
Influential Citations
30
Citations
Journal
Journal of molecular biology
Abstract
Abstract 9-Ethyl-2,6-diaminopurine forms 1:2 hydrogen-bonded complexes with 1-methylthymine and with 1-methyl-5-iodouracil. Both structures have been determined by three-dimensional X-ray diffraction methods and refined by block diagonal least squares. The first complex, 9-ethyl-2,6-diaminopurine: 1-methyl-thymine, exhibits both Watson-Crick and “reversed” Hoogsteen type base pairing configurations, while the second complex, 9-ethyl-2,6-diaminopurine: 1-methyl-5-iodouracil, involves both “reversed” Watson-Crick and Hoogsteen type base pairing configurations. These base pairing configurations may reflect differences in crystal lattice forces stabilizing these structures; however, an alternative possibility is that the observed configurations are particularly stable ones which reflect the strong associations between these compounds in solution before co-crystallization. If the latter is true, then the diaminopurine: iodouracil interaction involves a perturbation not present in the diaminopurine: thymine interaction, and this possibility is discussed in relation to previous structures described in this series.