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| {{STRUCTURE_285d| PDB=285d | SCENE= }} | | {{STRUCTURE_285d| PDB=285d | SCENE= }} |
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| '''X-RAY AND SOLUTION STUDIES OF DNA OLIGOMERS AND IMPLICATIONS FOR THE STRUCTURAL BASIS OF A-TRACT-DEPENDENT CURVATURE'''
| | ===X-RAY AND SOLUTION STUDIES OF DNA OLIGOMERS AND IMPLICATIONS FOR THE STRUCTURAL BASIS OF A-TRACT-DEPENDENT CURVATURE=== |
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| ==Overview==
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| DNA containing short periodic stretches of adenine residues (known as A-tracts), which are aligned with the helical repeat, exhibit a pronounced macroscopic curvature. This property is thought to arise from the cumulative effects of a distinctive structure of the A-tract. It has also been observed by gel electrophoresis that macroscopic curvature is largely retained when inosine bases are introduced singly into A-tracts but decreases abruptly for pure I-tracts. The structural basis of this effect is unknown. Here we describe X-ray and gel electrophoretic analyses of several oligomers incorporating adenine or inosine bases or both. We find that macroscopic curvature is correlated with a distinctive base-stacking geometry characterized by propeller twisting of the base-pairs. Regions of alternating adenine and inosine bases display large propeller twisting comparable to that of pure A-tracts, whereas the values observed for pure I-tracts are significantly smaller. We also observe in the crystal structures that propeller twist leads to close cross-strand contacts between amino groups from adenine and cytosine bases, indicating an attractive NH-N interaction, which is analogous to the NH-O interaction proposed for A-tracts. This interaction also occurs between adenine bases across an A-T step and may explain in part the different behavior of A-T versus T-A steps in the context of A-tract-induced curvature. We also note that hydration patterns may contribute to propeller-twisted conformation. Based on the present data and other structural and biophysical studies, we propose that DNA macroscopic curvature is related to the structural invariance of A-tract and A-tract-like regions conferred by high propeller twist, cross-strand interactions and characteristic hydration. The implications of these findings to the mechanism of DNA bending are discussed.
| | The line below this paragraph, {{ABSTRACT_PUBMED_9126841}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 9126841 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_9126841}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Double helix]] | | [[Category: Double helix]] |
| [[Category: Modified]] | | [[Category: Modified]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 18:25:23 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jul 28 05:35:35 2008'' |
