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| {{STRUCTURE_167d| PDB=167d | SCENE= }} | | {{STRUCTURE_167d| PDB=167d | SCENE= }} |
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| '''THE CRYSTAL STRUCTURE OF C-C-A-T-T-A-A-T-G-G: IMPLICATIONS FOR BENDING OF B-DNA AT T-A STEPS'''
| | ===THE CRYSTAL STRUCTURE OF C-C-A-T-T-A-A-T-G-G: IMPLICATIONS FOR BENDING OF B-DNA AT T-A STEPS=== |
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| ==Overview==
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| The single-crystal X-ray analysis of trigonal C-C-A-T-T-A-A-T-G-G, and its comparison with orthorhombic C-G-A-T-T-A-A-T-C-G, have shown that the A-T-T-A-A-T sequence has limited polymorphism under the influence of packing forces from neighboring molecules in the crystal. The T-A step is intrinsically variable. It is not inconsistent with a large propeller twist, a narrow minor groove, and a single spine of hydration, as has sometimes been claimed on theoretical grounds. The T-A step does show a persistent positive roll, in a direction that compresses the major groove, and this may be a significant factor in macroscopic DNA curvature induced by phased A-tracts. A-tracts, as understood in this paper, include A-A and A-T steps, but not the T-A step, which is disruptive. Three conclusions regarding A-tract-induced curvature can be drawn from this and other X-ray crystal structure analyses, and from key gel retardation experiments: (1) The A-tract bending model is disqualified on two grounds: (i) tilt-wedge bending within A-tracts is incompatible with the observed direction of curvature; (ii) roll-wedge bending within A-tracts is contradicted by every crystal structure analysis, and is inconsistent with gel retardation results for (G-C-A-A-A-A-T-T-T-T)n and for (A-A-A-A-A-T-T-T-T-T)n. (2) The junction bend model is contradicted by crystallography because: (i) the inclination of base-pairs does not change between A-tract and non-A-tract regions of helix; and (ii) the observed bends at GC/AT junctions are roll-wedge bends, not tilt-wedge as the junction bend model demands. (3) The non-A-tract bending model is consistent with both gel retardation data and with X-ray crystallography, and must be regarded as the only consistent model for A-tract bending. | | The line below this paragraph, {{ABSTRACT_PUBMED_8196049}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 8196049 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_8196049}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: B-dna]] | | [[Category: B-dna]] |
| [[Category: Double helix]] | | [[Category: Double helix]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 09:32:15 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jun 30 15:34:05 2008'' |