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R E Dickerson

Publications and source records attributed to R E Dickerson.

At least 55 records · Page 3Linked to original sources
PubMed1993

Crystal structure of CATGGCCATG and its implications for A-tract bending models.

The single-crystal x-ray analysis of orthorhombic CATGGCCATG has revealed a previously unrecognized mode of intrinsic bending in DNA. The decamer shows a smooth bend of 23 degrees over the central four base pairs, caused by preferential stacking interactions at guanine bases. The bend is produced by a roll of base pairs along their long axes, in a direction that compresses the wide major groove of the double helix. This major-groove-compressing bend at GGC, plus the abundant crystallographic evidence that runs of successive adenine bases (A-tracts) are straight and unbent, requires rethinking of the models most commonly invoked to explain A-tract bending. A decade of excellent experimental work involving gel migration experiments, cyclization kinetics, and nucleosome phasing has clearly established that introduction of short A-tracts into a general DNA sequence in synchrony with the natural repeat of the helix leads to bending. But it does not logically and inevitably follow that the actual bending is to be found within these introduced A-tracts or even at junctions with general-sequence B-DNA.

Base Composition↗
PubMed1993

Structure of the B-DNA decamer C-C-A-A-C-I-T-T-G-G in two different space groups: conformational flexibility of B-DNA.

For the first time, the same B-DNA oligomer has been crystallized and its structure solved in two different space groups. Crystallization of C-C-A-A-C-I-T-T-G-G with Ca2+ yields monoclinic space group C2 with a = 31.87 A, b = 25.69 A, c = 34.21 A, beta = 114.1 degrees, and five base pairs per asymmetric unit. The 5026 2 sigma data to 1.3 A refine to R = 0.152 with 72 waters, one heptavalent hydrated calcium complex, and one cacodylate ion per asymmetric unit. In contrast, crystallization with Mg2+ yields trigonal space group P3(2)21 with a = b = 33.23 A, c = 94.77 A, gamma = 120 degrees, and 10 base pairs per asymmetric unit. The 1725 2 sigma data to 2.2 A refine to R = 0.164 with 36 water molecules and one octahedral magnesium complex per asymmetric unit. The monoclinic form is virtually isostructural with previously solved monoclinic decamers, including twist angles of ca. 50 degrees at C-A and T-G steps. In contrast, the trigonal structure has quite different local helix parameters, with twist angles of ca. 36 degrees at the corresponding steps. These local parameter differences can only be attributed to crystal packing, suggesting that certain sequences of B-DNA are more flexible and influenced by their surroundings than had previously been thought. Such deformability may be important for interaction of B-DNA with control proteins, where both static structure and dynamic deformability comprise components of the recognition process. The crossing of two helices at an angle of 120 degrees in the trigonal cell is a model for an antiparallel, uncrossed Holliday junction, as has been noted earlier by Timsit and Moras [Timsit, Y., & Moras, D. (1991) J. Mol. Biol. 221, 919-940] from a rhombohedral DNA dodecamer structure analysis.

Base Composition↗
PubMed1992

Alternative structures for alternating poly(dA-dT) tracts: the structure of the B-DNA decamer C-G-A-T-A-T-A-T-C-G.

The X-ray crystal structure of the decamer C-G-A-T-A-T-A-T-C-G has been solved with two contrasting cations, Ca2+ and Mg2+. Crystals with calcium are space group P2(1)2(1)2(1), cell dimensions a = 38.76 A, b = 40.06 A, and c = 33.73 A, and diffract to 1.7-A resolution. Crystals with magnesium have the same space group, cell dimensions a = 38.69 A, b = 39.56 A, and c = 33.64 A, and diffract to 2.0 A. Their structures were solved independently by molecular replacement, beginning with idealized Arnott B-DNA geometry. The calcium structure refined to R = 17.8% for the 3683 reflections greater than 2 sigma, with 404 DNA atoms, 95 solvent peaks, and 1 Ca(H2O)7(2+) ion. The magnesium structure refined to R = 16.5% for the 1852 reflections greater than 2 sigma, with 404 DNA atoms, 62 solvent peaks, and 1 Mg(H2O)6(2+) ion. The two structures are virtually identical and are isostructural with C-G-A-T-C-G-A-T-C-G [Grzeskowiak et al. (1991) J. Biol. Chem. 266, 8861-8883] and C-G-A-T-T-A-A-T-C-G [Quintana et al. (1992) J. Mol. Biol. 225, 375-395]. Comparison of C-G-A-T-A-T-A-T-C-G with C-G-C-A-T-A-T-A-T-G-C-G [Yoon et al. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 6332-6336] shows that the expected alternation of twist angles is found in the central A-T-A-T-A-T region of the decamer (A-T small, T-A large), but the minor groove remains wide at the center, rather than narrow. Minor groove narrowing is produced, in these two structures, not by overwinding of the helix, but by an increase in base pair propeller. This analysis confirms the concept that poly(dA-dT).poly(dA-dT) is polymorphous, with different local conformations possible in different local environments.

Base Sequence↗
PubMed1992

Structure of a B-DNA decamer with a central T-A step: C-G-A-T-T-A-A-T-C-G.

The X-ray crystal structure analysis of the decamer C-G-A-T-T-A-A-T-C-G has been carried out to a resolution of 1.5 A. The crystals are space group P2(1)2(1)2(1), cell dimensions a = 38.60 A, b = 39.10 A, c = 33.07 A. The structure was solved by molecular replacement and refined with X-PLOR and NUCLSQ. The final R factor for a model with 404 DNA atoms, 108 water molecules and one magnesium hexahydrate cation is 15.7%. The double helix is essentially isostructural with C-G-A-T-C-G-A-T-C-G, with closely similar local helix parameters. The structure of the T-T-A-A center differs from that found in C-G-C-G-T-T-A-A-C-G-C-G in that the minor groove in our decamer is wide at the central T-A step rather than narrow, and the twist angle of the T-A step is small (31.1 degrees) rather than large. Whereas the tetrad model provides a convenient framework for discussing local DNA helix structure, it cannot be the entire story. The articulated helix model of DNA structure proposes that certain sequence regions of DNA show preferential twisting or bending properties, whereas other regions are less capable of deformation, in a manner that may be useful in sequence recognition by drugs and protein. Further crystal structure analyses should help to delineate the precise nature of sequence-dependent articulation in the DNA double helix.

Base Composition↗
PubMed1991

The molecular structure of wild-type and a mutant Fis protein: relationship between mutational changes and recombinational enhancer function or DNA binding.

The 98-amino acid Fis protein from Escherichia coli functions in a variety of reactions, including promotion of Hin-mediated site-specific DNA inversion when bound to an enhancer sequence. It is unique among site-specific DNA-binding proteins in that it binds to a large number of different DNA sequences, for which a consensus sequence is difficult to establish. X-ray crystal structure analyses have been carried out at 2.3 A resolution for wild-type Fis and for an Arg-89----Cys mutant that does not stimulate DNA inversion. Each monomer of the Fis dimer has four alpha-helices, A-D; the first 19 residues are disordered in the crystal. The end of each C helix is hydrogen bonded to the beginning of helix B' from the opposite subunit in what effectively is one long continuous, although bent, helix. The four helices, C, B', C', and B, together define a platform through the center of the Fis molecule: helices A and A' are believed to be involved with Hin recombinase on one side, and helices D and D' interact with DNA lying on the other side of the platform. Helices C and D of each subunit comprise a helix-turn-helix (HTH) DNA-binding element. The spacing of these two HTH elements in the dimer, 25 A, is too short to allow insertion into adjacent major grooves of a straight B-DNA helix. However, bending the DNA at discrete points, to an overall radius of curvature of 62 A, allows efficient docking of a B-DNA helix with the Fis molecule. The proposed complex explains the experimentally observed patterns of methylation protection and DNase I cleavage hypersensitivity. The x-ray structure accounts for the effects of mutations in the Fis sequence. Those that affect DNA inversion but not DNA binding are located within the N-terminal disordered region and helix A. This inversion activation domain is physically separated in the Fis molecule from the HTH elements and may specify a region of contact with the Hin recombinase. In contrast, mutations that affect HTH helices C and D, or interactions of these with helix B, have the additional effect of decreasing or eliminating binding to DNA.

Amino Acid Sequence↗
PubMed1991

Low-temperature crystallographic analyses of the binding of Hoechst 33258 to the double-helical DNA dodecamer C-G-C-G-A-A-T-T-C-G-C-G.

The crystal structure of the complex of Hoechst 33258 and the DNA dodecamer C-G-C-G-A-A-T-T-C-G-C-G has been solved from X-ray data collected at three different low temperatures (0, -25, and -100 degrees C). Such temperatures have permitted collection of higher resolution data (2.0, 1.9, and 2.0 A, respectively) than with previous X-ray studies of the same complex. In all three cases, the drug is located in the narrow central A-A-T-T region of the minor groove. Data analyses at -25 and -100 degrees C (each with a 1:1 drug/DNA ratio in the crystallizing solution) suggest a unique orientation for the drug. In contrast, two orientations of the drug were found equally possible at 0 degrees C with a 2:1 drug/DNA ratio in solution. Dihedral angles between the rings of Hoechst 33258 appear to change in a temperature-dependent manner. The drug/DNA complex is stabilized by single or bifurcated hydrogen bonds between the two N-H hydrogen-bond donors in the benzimidazole rings of Hoechst and adenine N3 and thymine O2 acceptors in the minor groove. A general preference for AT regions is conferred by electrostatic potential and by narrowing of the walls of the groove. Local point-by-point AT specificity follows from close van der Waals contacts between ring hydrogen atoms in Hoechst 33258 and the C2 hydrogens of adenines. Replacement of one benzimidazole ring by purine in a longer chain analogue of Hoechst 33258 could make that particular site GC tolerant in the manner observed at imidazole substitution for pyrrole in lexitropsins.

Base Composition↗
PubMed1991

The structure of B-helical C-G-A-T-C-G-A-T-C-G and comparison with C-C-A-A-C-G-T-T-G-G. The effect of base pair reversals.

The crystal structure of the DNA decamer C-G-A-T-C-G-A-T-C-G has been solved to a resolution of 1.5 A, with a final R-factor of 16.1% for 5,107 two-sigma reflections. Crystals are orthorhombic space group P2(1)2(1)2(1), with cell dimensions a = 38.93 A, b = 39.63 A, c = 33.30 A, and 10 base pairs/asymmetric unit. The final structure contains 404 DNA atoms, 142 water molecules treated as oxygen atoms, and two Mg(H2O)6(2+) complexes. Decamers stack atop one another to simulate continuous helical columns through the crystal, as with three previously solved monoclinic decamers, but the lateral contacts between columns are quite different in the orthorhombic and monoclinic cells. Narrow and wide regions of the minor groove exhibit a single spine or two ribbons of hydration, respectively, and the minor groove is widest when BII phosphate conformations are opposed diagonally across the groove. Phosphate conformation, in turn, appears to have a base sequence dependence. Twist, rise, cup, and roll are linked as has been observed in the three monoclinic decamers and can be characterized by high or low twist profiles. In all five known decamer crystal structures and eight representative dodecamers, a high twist profile is observed with G-C and G-A steps whereas all other R-R steps are low twist profiles (R = purine). A-T and A-C steps are intermediate in character whereas C-A and C-G exhibit behavior that is strongly influenced by the profiles of the preceding and following steps. When sufficient data are in hand, sequence/structure relationships for all helix parameters probably should be considered in a 4-base pair context. At this stage of limited information the problem is compounded because there are 136 unique 4-base steps x-A-B-y in a double helix as compared with only 10 2-base steps A-B.

Crystallography↗
PubMed1991

Crystal structure analysis of the B-DNA dodecamer CGTGAATTCACG.

The crystal structure of the DNA dodecamer C-G-T-G-A-A-T-T-C-A-C-G has been determined at a resolution of 2.5 A, with a final R factor of 15.8% for 1475 nonzero reflections measured at 0 degrees C. The structure is isomorphous with that of the Drew dodecamer, with the space group P2(1)2(1)2(1) and cell dimensions of a = 24.94 A, b = 40.78 A, and c = 66.13 A. The asymmetric unit contains all 12 base pairs of the B-DNA double helix and 36 water molecules. The structure of C-G-T-G-A-A-T-T-C-A-C-G is very similar to that of C-G-C-G-A-A-T-T-C-G-C-G, with no major alterations in helix parameters. Water peaks in the refined structure appear to represent a selection of peaks that were observed in the Drew dodecamer. The minor-groove spine of hydration at 2.5 A is fragmentary, but as Narendra et al. (1991) [Biochemistry (following paper in this issue)] have observed, lowering the temperature leads to a more complete representation of the spine.

Base Sequence↗
PubMed1991

Molecular dynamics simulation of the hydration shell of a B-DNA decamer reveals two main types of minor-groove hydration depending on groove width.

The conformation of the self-complementary B-DNA decamer C-C-A-A-C-G-T-T-G-G is known from a high-resolution x-ray crystal structure analysis. Molecular dynamics simulation of the hydration shell of the decamer has revealed two main types of minor-groove hydration, depending on groove width. The narrow part of the minor groove has a spine of hydration analogous to that described for the A + T-rich center of the minor groove in the dodecamer C-G-C-G-A-A-T-T-C-G-C-G [Drew, H. R. & Dickerson, R. E. (1981) J. Mol. Biol. 151, 535-556], the first hydration layer of which contains one water molecular per base pair. In contrast, in the wide part of the minor groove, each base is hydrated individually, water molecules lying predominantly in the base plane. In intermediate-width regions, preferred water-molecule sites are shifted away from the base plane in a 3'-to-5' direction. This shift becomes more pronounced as the minor groove narrows, until the two water molecules lie approximately midway between base pairs. If the minor groove is narrowed still further, it accommodates only one water molecule, and the hydration transforms to the well-known water spine. The observed pattern agrees with available crystallographic data and with our earlier calculations. The results confirm the assumption that preferred positions of water oxygens in the minor groove depend predominantly on groove width rather than on base sequence. However, the location of water hydrogens, and the network of hydrogen bonding, can depend on base sequence. We suggest a simple explanation of water-spine formation in the narrow minor groove of a random DNA sequence. The spine of hydration may be a property of the minor groove of overwound variants of B-DNA, the C and D forms, for which the middle part of the decamer C-C-A-A-C-G-T-T-G-G can serve as a model.

Base Sequence↗
PubMed1991

Structure of the B-DNA decamer C-C-A-A-C-G-T-T-G-G and comparison with isomorphous decamers C-C-A-A-G-A-T-T-G-G and C-C-A-G-G-C-C-T-G-G.

The crystal structure of the DNA decamer C-C-A-A-C-G-T-T-G-G has been solved to a resolution of 1.4 A, and is compared with the 1.3 A structure of C-C-A-A-G-A-T-T-G-G and the 1.6 A structure of C-C-A-G-G-C-C-T-G-G. All three decamers crystallize isomorphously in space group C2 with five base-pairs per asymmetric unit, and with decamer double helices stacked atop one another along the c axis in a manner that closely approximates a continuous B helix. This efficient stacking probably accounts for the high resolution of the crystal data. Comparison of the three decamers reveals the following. (1) Minor groove width is more variable than heretofore realized. Regions of A.T base-pairs tend to be narrower than average, although two successive A.T base-pairs alone may not be sufficient to produce narrowing. The minor groove is wider in regions where BII phosphate conformations are opposed diagonally across the groove. (2) Narrow regions of minor groove exhibit a zig-zag spine of hydration, as was first seen in C-G-C-G-A-A-T-T-C-G-C-G, whereas wide regions show two ribbons of water molecules down the walls, connecting base edge N or O with sugar O-4' atoms. Regions of intermediate groove width may accommodate neither pattern of hydration well, and may exhibit a less regular pattern of hydration. (3) Base-pair stacking is virtually identical at equivalent positions in the three decamers. The unconnected step from the top of one decamer helix to the bottom of the next helix is a normal helix step in all respects, except for the absence of connecting phosphate groups. (4) BII phosphate conformation require the unstacking of the two bases linked by the phosphate, but do not necessarily follow as an inevitable consequence of unstacking. They have an influence on minor groove width as noted in point (1) above. (5) Sugar ring pseudorotation P and main-chain torsion angle delta show an excellent correlation as given by the equation: delta = 40 degrees cos (P + 144 degrees) + 120 degrees. Although centered around C-2'-endo, the conformations in these B-DNA helices are distributed broadly from C-3'-exo to O-4'-endo, unlike the tighter clustering around C-3'-endo observed in A-DNA oligomer structures.

Base Composition↗
PubMed1991

Analysis of local helix geometry in three B-DNA decamers and eight dodecamers.

Local variations in B-DNA helix structure are compared among three decamers and eight dodecamers, which contain examples of all ten base-pair step types. All pairwise combinations of helix parameters are compared by linear regression analysis, in a search for internal relationships as well as correlations with base sequence. The primary conclusions are: (1) Three-center hydrogen bonds between base-pairs occur frequently in the major groove at C-C, C-A, A-A and A-C steps, but are less convincing at C-C and C-T steps in the minor groove. The requirements for large base-pair propeller are (1) that the base-pair should be A.T rather than G.C, and (2) that it be involved in a major groove three-center hydrogen bond with the following base-pair. Either condition alone is insufficient. Hence, a large propeller is expected at the leading base-pair of A-A and A-C steps, but not at A-T, T-A, C-A or C-C steps. (2) A systematic and quantitative linkage exists between helix variables twist, rise, cup and roll, of such strength that the rise between base-pairs can hardly be described as an independent variable at all. Two typical patterns of behavior are observed at steps from one base-pair to the next: high twist profile (HTP), characterized by high twist, low rise, positive cup and negative roll, and low twist profile (LTP), marked by low twist, high rise; negative cup and positive roll. Examples of HTP are steps G-C, G-A and Y-C-A-R, where Y is pyrimidine and R is purine. Examples of LTP steps are C-G, G-G, A-G and C-A steps other than Y-C-A-R. (3) The minor groove is especially narrow across the two base-pairs of the following steps: A-T, T-A, A-A and G-A. (4) In general, base step geometry cannot be correlated solely with the bases that define the step in question; the two flanking steps also must be taken into account. Hence, local helix structure must be studied in the context, not of two base-pairs: A-B, but of four: x-A-B-y. Calladine's rules, although too simple in detail, were correct in defining the length of sequence over which a given perturbation is expressed. Whereas ten different two-base steps are possible, allowing for the identity of complementary sequences, there are 136 different four-base steps. Only 33 of these 136 four-base steps are represented in the decamer and dodecamer structures solved to date, and hence it is premature to try to set up detailed structural algorithms. (5) The sugar-phosphate backbone chains of B-DNA place strong limits on sequence-induced structural variation, damping down most variables within four or five base-pairs, and preventing purine-purine anti-anti mismatches from causing bulges in the double helix. Hence, although short-range sequence-induced deformations (or deformability) are observed, long-range deformations propagated down the helix are not to be expected.

Base Composition↗
PubMed1990

Structure of a T4 hairpin loop on a Z-DNA stem and comparison with A-RNA and B-DNA loops.

The synthetic DNA oligomer C-G-C-G-C-G-T-T-T-T-C-G-C-G-C-G crystallizes as a Z-DNA hexamer, capped at one end by a T4 loop. The crystals are monoclinic, space group C2, with a = 57.18 A, b = 21.63 A, c = 36.40 A, beta = 95.22 degrees, and one hairpin molecule per asymmetric unit. The structure of the z-hexamer stem was determined by molecular replacement, and the T4 loop was positioned by difference map methods. The final R factor at 2.1 A resolution for hairpin plus 70 water molecules is 20% for 2 sigma data, with a root-mean-square error of 0.26 A. The (C-G)3 stem resembles the free Z-DNA hexamer with minor crystal packing effects. The T4 loop differs from that observed on a B-DNA stem in solution, or in longer loops in tRNA, in that it shows intraloop and intermolecular interactions rather than base stacking on the final base-pair of the stem. Bases T7, T8 and T9 stack with one another and with the sugar of T7. Two T10 bases from different molecules stack between the C1-G12 terminal base-pairs of a third and fourth molecule, to simulate a T.T "base-pair". Distances between thymine N and O atoms suggest that the two thymine bases are hydrogen bonded, and a keto-enol tautomer pair is favored over disordered keto-keto wobble pairs. The hairpin molecules pack in the crystal in herringbone columns in a manner that accounts well for the observed relative crystal growth rates in a, b and c directions. Hydration seems to be most extensive around the phosphate groups, with lesser hydration within the grooves.

Base Composition↗
PubMed1990

G-DNA: a twice-folded DNA structure adopted by single-stranded oligo(dG) and its implications for telomeres.

Our dimethyl sulfate modification experiments suggest that (dG)n stretches within single-stranded DNA fragments, which represent the simplest model for telomeric sequences, adopt a complex intrastrand structure other than a simple hairpin. We present a molecular model for the DNA structure that conforms to dimethyl sulfate methylation data. The principal element of this G-DNA structure is a quadruple helix formed by pairwise antiparallel segments of the twice-folded (dG)n stretch. This quadruple core has two wide and two narrow grooves connected by three loop-shaped segments. The strong stacking interactions of the neighboring guanine tetrads and the large number of hydrogen bonds formed can be the primary reasons that such structures are favored over a common hairpin for long (dG)n stretches. Such compact structures may be formed from (dG)n stretches of telomeric sequences.

Chromosomes↗
PubMed1990

Disordered single crystal evidence for a quadruple helix formed by guanosine 5'-monophosphate.

The disodium salt of guanosine 5'-monophosphate (5'-GMP) has been crystallized earlier in an orthorhombic array. We have obtained a new crystal form of 5'-GMP at pH 8 which reveals a clear helical nature, with guanine bases stacked perpendicular to the helix axis. Although the X-ray pictures show partial disorder, they can be indexed on a hexagonal net with a = b = 28.6 A, c = 9.8 A, V = 6942 A3 (1A = 0.1 nm). The probable space group is P6(4), and past experience with ca. 600 A3 per base in oligonucleotide crystals suggests that the cell contains 12 GMP molecules. The crystal packing parameters and the intensity distribution agree with a model of three hydrogen-bonded guanine tetrads in the unit cell, stacked so as to build a quadruple helix similar to that proposed earlier from fiber studies (Zimmerman, S.B., J. Mol. Biol. 106, 663-672 (1976)).

Fourier Analysis↗
PubMed1989

Definitions and nomenclature of nucleic acid structure components.

We report here recommendations for the definitions and nomenclature of nucleic acid structure parameters. These recommendations result from discussions at an EMBO Workshop on DNA Curvature and Bending held at Churchill College, Cambridge, in September 1988.

Base Composition↗