1
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Velmurugu Y, Vivas P, Connolly M, Kuznetsov SV, Rice PA, Ansari A. Two-step interrogation then recognition of DNA binding site by Integration Host Factor: an architectural DNA-bending protein. Nucleic Acids Res 2019; 46:1741-1755. [PMID: 29267885 PMCID: PMC5829579 DOI: 10.1093/nar/gkx1215] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 12/08/2017] [Indexed: 12/23/2022] Open
Abstract
The dynamics and mechanism of how site-specific DNA-bending proteins initially interrogate potential binding sites prior to recognition have remained elusive for most systems. Here we present these dynamics for Integration Host factor (IHF), a nucleoid-associated architectural protein, using a μs-resolved T-jump approach. Our studies show two distinct DNA-bending steps during site recognition by IHF. While the faster (∼100 μs) step is unaffected by changes in DNA or protein sequence that alter affinity by >100-fold, the slower (1–10 ms) step is accelerated ∼5-fold when mismatches are introduced at DNA sites that are sharply kinked in the specific complex. The amplitudes of the fast phase increase when the specific complex is destabilized and decrease with increasing [salt], which increases specificity. Taken together, these results indicate that the fast phase is non-specific DNA bending while the slow phase, which responds only to changes in DNA flexibility at the kink sites, is specific DNA kinking during site recognition. Notably, the timescales for the fast phase overlap with one-dimensional diffusion times measured for several proteins on DNA, suggesting that these dynamics reflect partial DNA bending during interrogation of potential binding sites by IHF as it scans DNA.
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Affiliation(s)
- Yogambigai Velmurugu
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Paula Vivas
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Mitchell Connolly
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Serguei V Kuznetsov
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Phoebe A Rice
- Department of Biochemistry & Molecular Biology, University of Chicago, Chicago, IL 60637, USA
| | - Anjum Ansari
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA.,Department of Bioengineering, University of Illinois at Chicago, Chicago, IL 60607, USA
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2
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Zhou HX, Pang X. Electrostatic Interactions in Protein Structure, Folding, Binding, and Condensation. Chem Rev 2018; 118:1691-1741. [PMID: 29319301 DOI: 10.1021/acs.chemrev.7b00305] [Citation(s) in RCA: 454] [Impact Index Per Article: 75.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Charged and polar groups, through forming ion pairs, hydrogen bonds, and other less specific electrostatic interactions, impart important properties to proteins. Modulation of the charges on the amino acids, e.g., by pH and by phosphorylation and dephosphorylation, have significant effects such as protein denaturation and switch-like response of signal transduction networks. This review aims to present a unifying theme among the various effects of protein charges and polar groups. Simple models will be used to illustrate basic ideas about electrostatic interactions in proteins, and these ideas in turn will be used to elucidate the roles of electrostatic interactions in protein structure, folding, binding, condensation, and related biological functions. In particular, we will examine how charged side chains are spatially distributed in various types of proteins and how electrostatic interactions affect thermodynamic and kinetic properties of proteins. Our hope is to capture both important historical developments and recent experimental and theoretical advances in quantifying electrostatic contributions of proteins.
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Affiliation(s)
- Huan-Xiang Zhou
- Department of Chemistry and Department of Physics, University of Illinois at Chicago , Chicago, Illinois 60607, United States.,Department of Physics and Institute of Molecular Biophysics, Florida State University , Tallahassee, Florida 32306, United States
| | - Xiaodong Pang
- Department of Physics and Institute of Molecular Biophysics, Florida State University , Tallahassee, Florida 32306, United States
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3
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Sinha K, Sangani SS, Kehr AD, Rule GS, Jen-Jacobson L. Metal Ion Binding at the Catalytic Site Induces Widely Distributed Changes in a Sequence Specific Protein-DNA Complex. Biochemistry 2016; 55:6115-6132. [PMID: 27786446 PMCID: PMC5402698 DOI: 10.1021/acs.biochem.6b00919] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
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Metal
ion cofactors can alter the energetics and specificity of
sequence specific protein–DNA interactions, but it is unknown
if the underlying effects on structure and dynamics are local or dispersed
throughout the protein–DNA complex. This work uses EcoRV endonuclease
as a model, and catalytically inactive lanthanide ions, which replace
the Mg2+ cofactor. Nuclear magnetic resonance (NMR) titrations
indicate that four Lu3+ or two La3+ cations
bind, and two new crystal structures confirm that Lu3+ binding
is confined to the active sites. NMR spectra show that the metal-free
EcoRV complex with cognate (GATATC) DNA is structurally distinct from
the nonspecific complex, and that metal ion binding sites are not
assembled in the nonspecific complex. NMR chemical shift perturbations
were determined for 1H–15N amide resonances,
for 1H–13C Ile-δ-CH3 resonances, and for stereospecifically assigned Leu-δ-CH3 and Val-γ-CH3 resonances. Many chemical
shifts throughout the cognate complex are unperturbed, so metal binding
does not induce major conformational changes. However, some large
perturbations of amide and side chain methyl resonances occur as far
as 34 Å from the metal ions. Concerted changes in specific residues
imply that local effects of metal binding are propagated via a β-sheet
and an α-helix. Both amide and methyl resonance perturbations
indicate changes in the interface between subunits of the EcoRV homodimer.
Bound metal ions also affect amide hydrogen exchange rates for distant
residues, including a distant subdomain that contacts DNA phosphates
and promotes DNA bending, showing that metal ions in the active sites,
which relieve electrostatic repulsion between protein and DNA, cause
changes in slow dynamics throughout the complex.
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Affiliation(s)
- Kaustubh Sinha
- Department of Biological Sciences, University of Pittsburgh , Pittsburgh, Pennsylvania 15260, United States.,Department of Biological Sciences, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Sahil S Sangani
- Department of Biological Sciences, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Andrew D Kehr
- Department of Biological Sciences, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Gordon S Rule
- Department of Biological Sciences, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Linda Jen-Jacobson
- Department of Biological Sciences, University of Pittsburgh , Pittsburgh, Pennsylvania 15260, United States
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4
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McHarris DM, Barr DA. Truncated variants of the GCN4 transcription activator protein bind DNA with dramatically different dynamical motifs. J Chem Inf Model 2014; 54:2869-75. [PMID: 25204850 DOI: 10.1021/ci500448e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The yeast protein GCN4 is a transcriptional activator in the basic leucine zipper (bZip) family, whose distinguishing feature is the "chopstick-like" homodimer of alpha helices formed at the DNA-binding interface. While experiments have shown that truncated versions of the protein retain biologically relevant DNA-binding affinity, we present the results of a computational study revealing that these variants show a wide variety of dynamical modes in their interaction with the target DNA sequence. We have performed all-atom molecular dynamics simulations of the full-length GCN4 protein as well as three truncated variants; our data indicate that the truncated mutants show dramatically different correlation patterns. We conclude that although the truncated mutants still retain DNA-binding ability, the bZip interface present in the full-length protein provides important stability for the protein-DNA complex.
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Affiliation(s)
- Danielle M McHarris
- Department of Chemistry and Biochemistry, Utica College , 1600 Burrstone Road, Utica, New York 13502, United States
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5
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Vivas P, Velmurugu Y, Kuznetsov SV, Rice PA, Ansari A. Global analysis of ion dependence unveils hidden steps in DNA binding and bending by integration host factor. J Chem Phys 2014; 139:121927. [PMID: 24089739 DOI: 10.1063/1.4818596] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Proteins that recognize and bind to specific sites on DNA often distort the DNA at these sites. The rates at which these DNA distortions occur are considered to be important in the ability of these proteins to discriminate between specific and nonspecific sites. These rates have proven difficult to measure for most protein-DNA complexes in part because of the difficulty in separating the kinetics of unimolecular conformational rearrangements (DNA bending and kinking) from the kinetics of bimolecular complex association and dissociation. A notable exception is the Integration Host Factor (IHF), a eubacterial architectural protein involved in chromosomal compaction and DNA recombination, which binds with subnanomolar affinity to specific DNA sites and bends them into sharp U-turns. The unimolecular DNA bending kinetics has been resolved using both stopped-flow and laser temperature-jump perturbation. Here we expand our investigation by presenting a global analysis of the ionic strength dependence of specific binding affinity and relaxation kinetics of an IHF-DNA complex. This analysis enables us to obtain each of the underlying elementary rates (DNA bending/unbending and protein-DNA association/dissociation), and their ionic strength dependence, even under conditions where the two processes are coupled. Our analysis indicates interesting differences in the ionic strength dependence of the bi- versus unimolecular steps. At moderate [KCl] (100-500 mM), nearly all the ionic strength dependence to the overall equilibrium binding affinity appears in the bimolecular association/dissociation of an initial, presumably weakly bent, encounter complex, with a slope SK(bi) ≈ 8 describing the loglog-dependence of the equilibrium constant to form this complex on [KCl]. In contrast, the unimolecular equilibrium constant to form the fully wrapped specific complex from the initial complex is nearly independent of [KCl], with SK(uni) < 0.5. This result is counterintuitive because there are at least twice as many ionic protein-DNA contacts in the fully wrapped complex than in the weakly bent intermediate. The following picture emerges from this analysis: in the bimolecular step, the observed [KCl]-dependence is consistent with the number of DNA counterions expected to be released when IHF binds nonspecifically to DNA whereas in the unimolecular reorganization step, the weak [KCl]-dependence suggests that two effects cancel one another. On one hand, formation of additional protein-DNA contacts in the fully wrapped complex releases bound counterions into bulk solution, which is entropically favored by decreasing [salt]. On the other hand, formation of the fully wrapped complex also releases tightly bound water molecules, which is osmotically favored by increasing [salt]. More generally, our global analysis strategy is applicable to other protein-DNA complexes, and opens up the possibility of measuring DNA bending rates in complexes where the unimolecular and bimolecular steps are not easily separable.
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Affiliation(s)
- Paula Vivas
- Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, USA
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6
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Sapienza PJ, Niu T, Kurpiewski MR, Grigorescu A, Jen-Jacobson L. Thermodynamic and structural basis for relaxation of specificity in protein-DNA recognition. J Mol Biol 2014; 426:84-104. [PMID: 24041571 PMCID: PMC3928799 DOI: 10.1016/j.jmb.2013.09.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Revised: 09/03/2013] [Accepted: 09/08/2013] [Indexed: 11/26/2022]
Abstract
As a novel approach to the structural and functional properties that give rise to extremely stringent sequence specificity in protein-DNA interactions, we have exploited "promiscuous" mutants of EcoRI endonuclease to study the detailed mechanism by which changes in a protein can relax specificity. The A138T promiscuous mutant protein binds more tightly to the cognate GAATTC site than does wild-type EcoRI yet displays relaxed specificity deriving from tighter binding and faster cleavage at EcoRI* sites (one incorrect base pair). AAATTC EcoRI* sites are cleaved by A138T up to 170-fold faster than by wild-type enzyme if the site is abutted by a 5'-purine-pyrimidine (5'-RY) motif. When wild-type protein binds to an EcoRI* site, it forms structurally adapted complexes with thermodynamic parameters of binding that differ markedly from those of specific complexes. By contrast, we show that A138T complexes with 5'-RY-flanked AAATTC sites are virtually indistinguishable from wild-type-specific complexes with respect to the heat capacity change upon binding (∆C°P), the change in excluded macromolecular volume upon association, and contacts to the phosphate backbone. While the preference for the 5'-RY motif implicates contacts to flanking bases as important for relaxed specificity, local effects are not sufficient to explain the large differences in ∆C°P and excluded volume, as these parameters report on global features of the complex. Our findings therefore support the view that specificity does not derive from the additive effects of individual interactions but rather from a set of cooperative events that are uniquely associated with specific recognition.
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Affiliation(s)
- Paul J Sapienza
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Tianyi Niu
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Michael R Kurpiewski
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Arabela Grigorescu
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Linda Jen-Jacobson
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA.
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7
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Spiriti J, Kamberaj H, de Graff AMR, Thorpe MF, van der Vaart A. DNA Bending through Large Angles Is Aided by Ionic Screening. J Chem Theory Comput 2012; 8:2145-56. [PMID: 26593845 DOI: 10.1021/ct300177r] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
We used adaptive umbrella sampling on a modified version of the roll angle to simulate the bending of DNA dodecamers. Simulations were carried out with the AMBER and CHARMM force fields for 10 sequences in which the central base pair step was varied. On long length scales, the DNA behavior was found to be consistent with the worm-like chain model. Persistence lengths calculated directly from the simulated structures and indirectly through the use of sequence-independent coarse-grained models based on simulation data were similar to literature values. On short length scales, the free energy cost of bending DNA was found to be consistent with the worm-like chain model for small and intermediate bending angles. At large angles, the bending free energy as a function of the roll angle became linear, suggesting a relative increase in flexibility at larger roll angles. Counterions congregated on the concave side of the highly bent DNA and screened the repulsion of the phosphate groups, facilitating the bending.
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Affiliation(s)
- Justin Spiriti
- Department of Chemistry, University of South Florida, 4202 E Fowler Ave. CHE 205, Tampa, Florida 33620, United States
| | - Hiqmet Kamberaj
- Faculty of Technical Sciences, International Balkan University, Skopje, Republic of Macedonia
| | - Adam M R de Graff
- Center for Biological Physics, Arizona State University, Tempe, Arizona 85287, United States.,Department of Physics, Arizona State University, P.O. Box 871504, Tempe, Arizona 85287, United States.,Laufer Center for Physical and Quantitative Biology, Stony Brook University, Stony Brook, New York 11794, United States
| | - M F Thorpe
- Center for Biological Physics, Arizona State University, Tempe, Arizona 85287, United States.,Department of Physics, Arizona State University, P.O. Box 871504, Tempe, Arizona 85287, United States
| | - Arjan van der Vaart
- Department of Chemistry, University of South Florida, 4202 E Fowler Ave. CHE 205, Tampa, Florida 33620, United States
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8
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ESR spectroscopy identifies inhibitory Cu2+ sites in a DNA-modifying enzyme to reveal determinants of catalytic specificity. Proc Natl Acad Sci U S A 2012; 109:E993-1000. [PMID: 22493217 DOI: 10.1073/pnas.1200733109] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The relationship between DNA sequence recognition and catalytic specificity in a DNA-modifying enzyme was explored using paramagnetic Cu(2+) ions as probes for ESR spectroscopic and biochemical studies. Electron spin echo envelope modulation spectroscopy establishes that Cu(2+) coordinates to histidine residues in the EcoRI endonuclease homodimer bound to its specific DNA recognition site. The coordinated His residues were identified by a unique use of Cu(2+)-ion based long-range distance constraints. Double electron-electron resonance data yield Cu(2+)-Cu(2+) and Cu(2+)-nitroxide distances that are uniquely consistent with one Cu(2+) bound to His114 in each subunit. Isothermal titration calorimetry confirms that two Cu(2+) ions bind per complex. Unexpectedly, Mg(2+)-catalyzed DNA cleavage by EcoRI is profoundly inhibited by Cu(2+) binding at these hitherto unknown sites, 13 Å away from the Mg(2+) positions in the catalytic centers. Molecular dynamics simulations suggest a model for inhibition of catalysis, whereby the Cu(2+) ions alter critical protein-DNA interactions and water molecule positions in the catalytic sites. In the absence of Cu(2+), the Mg(2+)-dependence of EcoRI catalysis shows positive cooperativity, which would enhance EcoRI inactivation of foreign DNA by irreparable double-strand cuts, in preference to readily repaired single-strand nicks. Nonlinear Poisson-Boltzmann calculations suggest that this cooperativity arises because the binding of Mg(2+) in one catalytic site makes the surface electrostatic potential in the distal catalytic site more negative, thus enhancing binding of the second Mg(2+). Taken together, our results shed light on the structural and electrostatic factors that affect site-specific catalysis by this class of endonucleases.
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9
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Koroleva ON, Volkov EM, Drutsa VL. Interaction of Escherichia coli RNA polymerase with artificial promoters, containing nonnucleotide spacers. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2011; 30:667-79. [PMID: 21888555 DOI: 10.1080/15257770.2011.598490] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
To study the functional role of the spacer region between two consensus -10 and -35 elements of promoters, recognized by E. coli RNA polymerase, the model promoter-like DNA duplexes containing nonnucleotide inserts (mimicking 17-mer spacer) either in one or both strands, were constructed. The modified duplexes can form the heparin-resistant binary complexes with RNA polymerase. The DNA duplex with nonnucleotide insert in the template strand can specifically direct the synthesis of mRNA in the in vitro run-off transcription assays.
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Affiliation(s)
- Olga Nikolaevna Koroleva
- Chemical Department, M. V. Lomonosov Moscow State University, 119992, Moscow, Russian Federation.
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10
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Binding and cleavage of DNA with the restriction enzyme EcoR1 using time-resolved second harmonic generation. Proc Natl Acad Sci U S A 2011; 108:19979-84. [PMID: 22114185 DOI: 10.1073/pnas.1115498108] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The binding of EcoR1 to a 90-bp DNA duplex attached to colloidal microparticles and the subsequent cleavage by the enzyme was observed in real time and label-free with time-resolved second harmonic (SH) spectroscopy. This method provides a unique way to investigate biomolecular interactions based on its sensitivity to changes in structure and electrical charge on formation of a complex and subsequent dynamics. The binding of EcoR1 to the recognition sequence in DNA appears as a rapid increase in the SH signal, which is attributed to the enzyme-induced change in the DNA conformation, going from a rod-like to a bent shape. In the presence of the cofactor Mg(2+), the subsequent decay in the SH signal was monitored in real time as the following processes occurred: cleavage of DNA, dissociation of the enzyme from the DNA, and diffusion of the 74-bp fragment into the bulk solution leaving the 16-bp fragment attached to the microparticle. The observed decay was dependent on the concentration of Mg(2+), which functions as a cofactor and as an electrolyte. With SH spectroscopy the rehybridization dynamics between the rehybridized microparticle bound and free cleaved DNA fragments was observed in real time and label-free following the cleavage of DNA. Collectively, the experiments reported here establish SH spectroscopy as a powerful method to investigate equilibrium and time-dependent biological processes in a noninvasive and label-free way.
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11
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Sidorova NY, Muradymov S, Rau DC. Solution parameters modulating DNA binding specificity of the restriction endonuclease EcoRV. FEBS J 2011; 278:2713-27. [PMID: 21624054 DOI: 10.1111/j.1742-4658.2011.08198.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The DNA binding stringency of restriction endonucleases is crucial for their proper function. The X-ray structures of the specific and non-cognate complexes of the restriction nuclease EcoRV are considerably different suggesting significant differences in the hydration and binding free energies. Nonetheless, the majority of studies performed at pH 7.5, optimal for enzymatic activity, have found a < 10-fold difference between EcoRV binding constants to the specific and nonspecific sequences in the absence of divalent ions. We used a recently developed self-cleavage assay to measure EcoRV-DNA competitive binding and to evaluate the influence of water activity, pH and salt concentration on the binding stringency of the enzyme in the absence of divalent ions. We find the enzyme can readily distinguish specific and nonspecific sequences. The relative specific-nonspecific binding constant increases strongly with increasing neutral solute concentration and with decreasing pH. The difference in number of associated waters between specific and nonspecific DNA-EcoRV complexes is consistent with the differences in the crystal structures. Despite the large pH dependence of the sequence specificity, the osmotic pressure dependence indicates little change in structure with pH. The large osmotic pressure dependence means that measurement of protein-DNA specificity in dilute solution cannot be directly applied to binding in the crowded environment of the cell. In addition to divalent ions, water activity and pH are key parameters that strongly modulate binding specificity of EcoRV.
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Affiliation(s)
- Nina Y Sidorova
- Laboratory of Physical and Structural Biology, Program of Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-0924, USA.
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12
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Holmquist PC, Holmquist GP, Summers ML. Comparing binding site information to binding affinity reveals that Crp/DNA complexes have several distinct binding conformers. Nucleic Acids Res 2011; 39:6813-24. [PMID: 21586590 PMCID: PMC3159480 DOI: 10.1093/nar/gkr369] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
We show that the cAMP receptor protein (Crp) binds to DNA as several different conformers. This situation has precluded discovering a high correlation between any sequence property and binding affinity for proteins that bend DNA. Experimentally quantified affinities of Synechocystis sp. PCC 6803 cAMP receptor protein (SyCrp1), the Escherichia coli Crp (EcCrp, also CAP) and DNA were analyzed to mathematically describe, and make human-readable, the relationship of DNA sequence and binding affinity in a given system. Here, sequence logos and weight matrices were built to model SyCrp1 binding sequences. Comparing the weight matrix model to binding affinity revealed several distinct binding conformations. These Crp/DNA conformations were asymmetrical (non-palindromic).
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Affiliation(s)
- Peter C Holmquist
- Department of Biology, California State University Northridge, 18111 Nordhoff St. Northridge, CA 91330, USA.
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