Atomic force microscopy imaging and pulling of nucleic acids
Helen G Hansma1, Kenichi Kasuya1,2 and Emin Oroudjev1
Recent advances in atomic force microscopy (AFM) imaging
of nucleic acids include the visualization of DNA and RNA
incorporated into devices and patterns, and into structures
based on their sequences or sequence recognition. AFM
imaging of nuclear structures has contributed to advances in
telomere research and to our understanding of nucleosome
formation. Highlights of force spectroscopy or pulling of nucleic
acids include the use of DNA as a programmable force sensor,
and the analysis of RNA flexibility and drug binding to DNA.
Addresses
1
Department of Physics, University of California, Santa Barbara,
CA 93106, USA
2
Department of Biological and Chemical Engineering, Faculty of
Engineering, Gunma University, 1-5-1 Tenjin, Kiryu-shi,
Gunma 376-8515, Japan
e-mail: [email protected]
Current Opinion in Structural Biology 2004, 14:380–385
This review comes from a themed issue on
Nucleic acids
Edited by Carlos Bustamante and Juli Feigon
Available online 19th May 2004
0959-440X/$ – see front matter
ß 2004 Elsevier Ltd. All rights reserved.
DOI 10.1016/j.sbi.2004.05.005
Abbreviations
AFM
atomic force microscopy/microscope
bp
base pairs
ds
double-stranded
MMTV mouse mammary tumor virus
ss
single-stranded
Introduction
Today’s research on atomic force microscopy (AFM)
imaging of nucleic acids differs from earlier research in
that the AFM images are much more likely to be simply
an adjunct to exciting research, instead of being an end
in themselves. Thus, this review emphasizes the science
being done, rather than the varieties of AFM methodology that were used.
For the benefit of readers not familiar with the AFM, this
instrument was invented in 1986 [1] and the visualization
of DNA was one of its first biological applications. The
AFM works by feeling the surface of a sample with such a
discriminating touch that it can sometimes even sense the
individual atoms on the surface of a crystal such as gold.
The AFM does this by raster-scanning a small tip back
and forth over the sample surface. The tip is on the end of
Current Opinion in Structural Biology 2004, 14:380–385
a cantilever, which deflects when the tip encounters
features on the sample surface. This deflection is sensed
with an optical lever; a laser beam reflecting off the end
of the cantilever onto a segmented photodiode magnifies
small cantilever deflections into large changes in the
relative intensity of the laser light on the two segments
of the photodiode. In this way, the AFM makes a topographic map of the sample surface.
This review covers some of the 271 papers published on
AFM imaging of nucleic acids in 2002 and 2003, as
gathered from the PubMed and Current Contents databases. Yuri Lyubchenko and his collaborators, in particular Luda Shlyakhtenko, are the current leaders in the
production of large quantities of good research on AFM
imaging of nucleic acids. DNA papers outnumber RNA
papers by about 10 to 1, which is much different from the
overall ratio of 2 to 1 or smaller for all DNA and RNA
papers in PubMed. It is increasingly difficult to select
from among these papers, as the overall quality of AFM
research has risen so much over the past several years. The
sections that follow represent only a small selection of the
many recent highlights in probe microscopy of nucleic
acids. The selectivity of this review also eliminates key
early research, on which this recent research is often based.
Nucleic acids in devices and patterns
Designer nucleic acids are being used to create ‘nanofabrics’ with amazing patterns resembling stripes and
plaids. Some of the newest patterns made with designer
nucleic acids are known as ‘waffles’ [2] and ‘barcodes’ [3]
(Figure 1). The father of this field, Ned Seeman, has most
recently developed a DNA rotary device, in collaboration
with a new leader in the field, Hao Yan, and other
colleagues [4]. AFM is a wonderful boon to this research,
because the direct visualization of these nano-structures
provides valuable information about their substructures,
defects and heterogeneity that cannot be obtained as
easily by any other technique.
Patterns and patterning of DNA
DNA waffles are assembled from four-arm junctions, each
of which contains nine oligonucleotides — two oligonucleotides form each arm and one oligonucleotide ‘knits’
the four arms together. Similar four-arm junctions form
tubular ‘nano-ribbons’. In waffles (Figure 1a), the fourarm junctions are connected alternately ‘face up’ and
‘face down’, whereas nano-ribbons contain four-arm junctions that are all facing in the same direction [2].
The bars in DNA barcodes (Figure 1b) are created by
the presence or absence of protruding hairpin loops [3].
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AFM imaging and pulling of nucleic acids Hansma, Kasuya and Oroudjev 381
Figure 1
DNA waffles (a) and DNA barcodes (b) are shown in these images (400 400 nm). The periodicity of the waffle grids in (a) is 19 nm.
Modified from [2,3].
Hairpin loops also feature in the construction of new
designer RNAs called ‘tectoRNAs’. In tectoRNAs, hairpin
loops base pair with other RNA oligonucleotides to provide some of the links in these structures. In nature, RNAs
have a wider range of structures and functions than DNAs;
the designers of tectoRNAs predict a similar versatility for
their synthetic structures [5]. Unlike DNA, RNA typically forms elaborate looped structures that interact with
each other and it can even function as an enzyme; interacting loops are already being incorporated into tectoRNAs and enzymatic activities may be incorporated
into future tectoRNAs to provide a regulatory function.
(SWNT) is attached to the RecA-coated region of the
DNA strand, using a streptavidin-functionalized SWNT
on a ‘sandwich filling’ of anti-RecA antibody and a
biotinylated secondary antibody [8].
Also in the ‘device’ category is a ‘non-device’. Noncontact AFM scans of DNA and carbon nanotubes in
contact with a gold electrode show that the carbon nanotube is a conductor, whereas the DNA is not and, therefore, cannot be used as a molecular wire unless it has been
metalized [9].
In the nucleus
Nanolithography is another approach to the patterning of
nucleic acids on surfaces. In direct-write dip-pen nanolithography (DPN), DNA is transferred from an AFM tip
to a substrate in a pattern traced by the x-y path of the
AFM tip on the substrate [6]. The procedure has been
improved to make the transfer of DNA ‘ink’ more like
writing with a fountain pen and less like writing with a
quill pen. This ink writes well on a gold substrate.
DNA devices
The patterning of DNA is increasingly being linked to
the creation of DNA devices. DNA nano-ribbons, for
example, are scaffolds for the formation of gold nanowires; and DNA waffles, when biotinylated, provide a
two-dimensional array of sites for streptavidin binding [2].
A clever sequence-specific method for coating DNA with
gold uses RecA-coated ssDNA that is complementary to
a sequence of dsDNA [7]. Homologous recombination
produces dsDNA interrupted by the bound RecA–
ssDNA complex. The bare dsDNA is metalized, which
creates a linear device consisting of discontinuous gold
nanowires.
A variation of this technique may be used to build a fieldeffect transistor (FET). A single-walled carbon nanotube
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Nucleosomes
Chromosome structure plays a crucial role in the processes of replication, repair and transcription in eukaryotes. Nucleosomes are the basic element of chromosome
organization. Nucleosomes reconstituted in vitro have
been visualized and analyzed by AFM during the past
decade. Recent data provide useful new information to
increase our understanding of chromosomes.
Zhang et al. [10] visualized the dynamic process of nucleosome reconstitution by slowly reducing the salt concentration. When the concentration of NaCl was decreased
from 1 to 0.65 M, DNA started binding to histone octamers. When the concentration of NaCl was reduced to
50 mM, the classical ‘beads-on-a-string’ structure of
nucleosomes could be clearly visualized using AFM.
Yodh et al. [11] used AFM to visualize the reconstitution
of nucleosomes on a repeated sequence of 5S rDNA.
They used both non-acetylated and hyperacetylated
HeLa histones at various subsaturating levels. The most
striking result was that non-acetylated histones showed
cooperativity of nucleosome positioning on the DNA,
whereas hyperacetylated histones showed no such cooperativity. Thus, acetylation of N-terminal histone tails
abolished the cooperativity of nucleosome positioning.
Current Opinion in Structural Biology 2004, 14:380–385
382 Nucleic acids
Nucleosome reconstitution on mouse mammary tumor
virus (MMTV) promoter DNA as a template was compared with that on 5S rDNA [12]. On the MMTV DNA,
nucleosomes tended to be formed pairwise and showed
relatively high salt stability. When average occupation
levels exceeded approximately eight nucleosomes per
template, MMTV arrays showed a significant level of
intramolecular compaction. This was not observed in
5S rDNA arrays. Thus, nucleosome formation can be
affected by the DNA sequence.
Using AFM, Hizume et al. [13] observed the in vitro
reconstitution of nucleosomes on a long DNA template
with a super-helical constraint. Nucleosomes on this
template condensed almost twice as much DNA
(290 bp/nucleosome) as on a DNA template without a
super-helical constraint (160 bp/nucleosome). The efficiency of nucleosome formation on the supercoiled DNA
was close to the in vivo efficiency, suggesting that reconstitution on the supercoiled DNA template reflects the
in vivo chromosome structure.
Sequence-dependent structures
In preparing samples of the GC-repeating dsDNA
poly(dG-dC)(dG-dC) (GC-DNA), a Ni(II)-containing
solution was used to bind the DNA to mica. Unexpectedly,
many toroids and other DNA condensates formed (Figure 2). These condensates were absent in poly(dA-dT)
(dA-dT) (AT-DNA). The clue to understanding this result
came from the electrostatic zipper theory of DNA condensation [17], coupled to the specificity of Ni(II) for
binding to the N7 of guanine. The GC-DNA had converted to Z-DNA in Ni(II), whereas AT-DNA was still
B-DNA. Electrostatic zipper calculations for Z-DNA, and
for the low salt solutions used in the AFM experiments,
showed that these sequence-dependent results could be
explained by a modified electrostatic zipper theory [18].
GC-DNA and AT-DNA are specialized examples of DNA
sequences characterized by alternating pyrimidines and
purines (Pyr/Pur). Long Pyr/Pur sequences occur with an
unusually high frequency in eukaryotic genomes. Mirrorimage Pyr/Pur sequences can form triple-helical structures, which appear as thickened regions in the AFM [19].
Telomeres
The multi-kilobase repeating hexameric telomere
sequence (TTAAGGG)n exists at the ends of chromosomes in eukaryotes. In vivo, telomeres are synthesized
by a reverse transcriptase telomerase, which is very
unstable in vitro. Therefore, artificial telomeres have
been synthesized by DNA polymerases using a DNA
nanocircle template that encoded the human telomere
sequence [14]. AFM imaging showed that the synthetic
telomeric single strands were up to 0.5 mm in length and
the polymerases that synthesized the strand remain
bound at the end. This model system could also extend
the telomeres of human chromosomes in fixed cells.
These results suggest that the combination of a DNA
polymerase and a nanocircle template effectively mimics
the natural ribonucleoprotein, which includes telomerase
and the telomerase RNA template.
Nuclear pores
Amazing AFM images show material, apparently mRNA,
exiting from pores in the nuclear membrane [15].
Sequence recognition and
sequence-dependent structures
Sequence recognition
The inorganic mineral surface of mica shows a highly
selective preference for one side of intrinsically curved
DNA containing A-tracts. In DNA containing short
A-tracts, the adenines tend to be positioned on one side
and the thymines tend to be positioned on the other side of
the DNA molecule. This DNA preferentially binds to mica
with the T-rich side facing down [16]. Selectivity was high
— up to 90% of the DNA molecules attached to the mica
with the T-rich side facing down, even when the DNA was
constructed so that it would form a C-shape in solution.
Current Opinion in Structural Biology 2004, 14:380–385
Abnormal DNA repeats are a common feature of many
genetic diseases. The structures of these repeats —open
DNA loops and condensed DNA segments — have been
visualized by AFM and used to propose a mechanism
by which the abnormal repeats might cause aberrant
replication [20].
The effects of ions and ligands
Ionic effects
Mg(II) and other divalent cations — Ca(II), Mn(II) and
Zn(II) — stabilize end-to-end interactions of stickyended DNA, whereas Na(I) is quite ineffective at stabilizing these interactions [21]. AFM images of blunt-end
DNA showed few end-to-end interactions even in Mg(II).
Supercoiling brings distant regions of dsDNA into close
contact. High salt concentrations increase the lengths of
DNA that are in close contact with each other. In high salt
(200 mM NaCl), 56 nm long stretches of DNA were in
close contact with each other, compared with 36 nm long
DNA in 50 mM NaCl [22].
Ligand effects
A chiral supramolecular ligand caused significant conformational changes in dsDNA upon the binding of one
enantiomer of the ligand but not the other [23]. This is
reasonable, as DNA is chiral. This work bridges the gap in
the study of non-covalent DNA binding by small ligands
that bind 1–3 bp of DNA and large ligands. The ligand, an
Fe(II)-chelated triple-helical cylinder, appears to bind
approximately 10 bp of DNA or one turn of the DNA
helix. DNA images provided a dramatic illustration of the
different effects of the enantiomers on the DNA structure. Data from melting curves were much less dramatic.
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AFM imaging and pulling of nucleic acids Hansma, Kasuya and Oroudjev 383
Figure 2
The bundle size of condensed GC-DNA [poly(dG-dC)(dG-dC)] is comparable in these two images, even though condensation in Ni(II) occurred
for 2 months in (a) and for only 3–5 min in (b). Something must be limiting the size of the condensates, which continue to grow through networking,
even though the bundle size remains constant (see [18]).
DNA–protein interactions
Protein interactions with DNA have been a fruitful area of
research since the early years of biological AFM. Typically, the protein is readily identified with reasonable
reliability as a ‘blob’ on the DNA; one can measure
the bend angle of the DNA at the protein-binding site
and the length of the DNA in complex with the protein,
compared with the uncomplexed DNA. The change in
length of the DNA upon binding the protein gives an
indication of the extent to which the DNA is looped
within or wrapped around the protein. The extent of
wrapping was investigated recently for DNA in complex
with two different RNA polymerases [24]. Newly synthesized RNA was also visible; this single strand was surprisingly similar to dsDNA in its approximate size and
persistence length.
populations — one bent and one unbent. It is hypothesized that MutS binds non-specifically to dsDNA and
bends it, searching for a mismatch, and that MutS complexes at the mismatch site evolve into a kinked complex,
consistent with X-ray crystallographic data, and then to an
unbent complex.
Force spectroscopy (pulling) of nucleic acids
Recent reviews present information gained about DNA
repair processes [25] and transcription in prokaryotes
using AFM [26]. The volumes of protein–DNA complexes, as measured from AFM images, were linearly
related to protein molecular weights over the range
41–670 kDa. Monomeric and dimeric protein complexes
were identified in this way [25].
Force changes in the pico-Newton (pN) and nanoNewton (nN) range upon extension of single nucleic acid
molecules can be studied by AFM instruments at a
resolution of about 5pN [28]. The forced extension of
one dsDNA molecule gives a force versus extension
curve (or spectrum) with easily identifiable features.
Specifically, the large force plateau that separates the
first and second stretching phases near 65 pN indicates
the transition of B-DNA into S-DNA (stretched DNA);
the double-helix structure of B-DNA is progressively
destroyed due to the loss of base stacking interactions.
The ratio of the first and second stretching phases is
called the S-value and is used to assess the relative
changes in contour length of the molecule after the first
transition [29]. The second force plateau near 150 pN
indicates the melting of dsDNA into ssDNA.
DNA bending and unbending by MutS proteins affects
the recognition of base pair mismatches [27]. MutS complexes with normal dsDNA were bent, whereas MutS
complexes with mismatched DNA sites showed two
Krautbauer and co-workers [30] investigated the effect
of the binding of three different small-molecule drugs to
dsDNA. The force versus extension spectra for dsDNA
alone and for each drug–DNA complex displayed changes
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Current Opinion in Structural Biology 2004, 14:380–385
384 Nucleic acids
that were characteristic of the particular drug–DNA
interaction mode. These changes were also dependent
on the drug concentration. The results confirm that AFMbased force spectroscopy can be effectively used to study
the basic mechanisms of DNA–drug interaction. The
authors mention the possibility of using such a system
in massive screening and/or sensing applications.
Conventional AFM-based rupture force spectroscopy has
been extended to a new method that the authors call the
‘differential force test’ [31]. In this method, a reference
bond (the nucleic acid duplex) is placed in series with a
bond of interest (a different nucleic acid duplex). During
the extension cycle, the weaker bond has a higher chance
of rupture. By determining which bond (which nucleic
acid duplex) survived during extension, researchers were
able to directly compare rupture forces for different DNA
duplexes. The sensitivity of the method was high enough
to detect a single base pair mismatch in a 20 bp duplex.
The authors also demonstrate that shear ruptures can be
easily distinguished from unzipping ruptures, proving that
this method is sensitive to the direction of the rupture
forces as well. The authors indicate that, after appropriate
modifications, this approach can be applied to arrays of
DNAs and proteins to discriminate between specific and
non-specific interactions of each tag–target pair.
Under single-molecule extension in AFM force spectroscopy experiments, dsRNA molecules demonstrate differences from the behavior of dsDNA molecules [29].
The only force plateau on the dsRNA force versus extension spectra indicates the transition of A0 -RNA into
S-RNA. The melting plateau was not detected in the
dsRNA spectra, indicating that melting forces for dsRNA
probably exceed the typical 200 pN forces at which the
molecule separates from the probe tip or the sample
surface. Another profound difference was observed in
the forces for the first transition plateau (B-DNA to
S-DNA transition for dsDNA and A0 -RNA to S-RNA
transition for dsRNA). Average plateau forces were 20%
higher for dsRNA molecules than for dsDNA molecules
with a similar base composition. The distribution of the
plateau forces was also much broader among individual
dsRNA molecules. The authors attribute the increase in
plateau forces to the significantly higher energy of base
stacking interactions in the A0 form of dsRNA.
Additional work on the stretching of single nucleic acid
molecules is also presented in this issue [32].
Conclusions
It is frustrating to find so many more excellent papers than
can be covered in this short review. With apologies to the
authors of these many uncited papers, this review will
close with a brief mention of another set of papers that are
also worthy of citation. Researchers in less affluent
nations face additional challenges in doing publishable
Current Opinion in Structural Biology 2004, 14:380–385
scientific research. For this reason, it is worth citing work
from Mexico [33], Slovakia [34], South Korea [35] and
Russia [36]. These papers show novel ribonucleoprotein
granules from the nuclei of Ginko cells [33], oddly kinked
DNA plasmids from Escherichia coli grown at 508C [34],
amino-silane surfaces for the deposition of DNA microarrays [35] and protein-mediated potato virus X disassembly [36]. These papers also illustrate the great diversity of
new applications of AFM in nucleic acid research.
Acknowledgements
This work was supported by National Science Foundation grant
MCB0236093 to HH.
References and recommended reading
Papers of particular interest, published within the annual period of
review, have been highlighted as:
of special interest
of outstanding interest
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Hansma HG, Oroudjev E, Baudrey S, Jaeger L: TectoRNA and
‘kissing-loop’ RNA: atomic force microscopy of selfassembling RNA structures. J Microsc 2003, 212:273-279.
This paper includes a tutorial that presents approaches to measuring
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6.
Demers LM, Ginger DS, Park SJ, Li Z, Chung SW, Mirkin CA:
Direct patterning of modified oligonucleotides on metals
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In this procedure for dip-pen nanolithography, the AFM tip is silylated by
treatment for 1 hr in a 1% solution of 3-aminopropyltrimethoxysilane in
toluene, followed by a 10 s dip into a DNA-containing ‘ink’ of 1 mM
hexane-thiol-modified DNA oligonucleotides in 90% dimethylformamide/
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dsDNA was pretreated with glutaraldehyde to create aldehyde-derivatized DNA, which was stretched on a passivated silicon substrate. In an
AgNO3 solution, silver aggregates form on the aldehydes of the unprotected dsDNA. The silver aggregates serve as catalysts for gold deposition, creating linear devices consisting of discontinuous gold nanowires.
8.
Keren K, Berman RS, Buchstab E, Sivan U, Braun E:
DNA-templated carbon nanotube field-effect transistor.
Science 2003, 302:1380-1382.
This beautiful work is an exciting extension of the work described in [7].
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Gomez-Navarro C, Moreno-Herrero F, de Pablo PJ, Colchero J,
Gomez-Herrero J, Baro AM: Contactless experiments on
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and its binding patterns with HMG1/2 and HMG14/17 proteins.
Cell Res 2003, 13:351-359.
11. Yodh JG, Woodbury N, Shlyakhtenko LS, Lyubchenko YL, Lohr D:
Mapping nucleosome locations on the 208-12 by AFM provides
clear evidence for cooperativity in array occupation.
Biochemistry 2002, 41:3565-3574.
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AFM imaging and pulling of nucleic acids Hansma, Kasuya and Oroudjev 385
12. Bash R, Wang H, Yodh J, Hager G, Lindsay SM, Lohr D:
Nucleosomal arrays can be salt-reconstituted on a single-copy
MMTV promoter DNA template: their properties differ in several
ways from those of comparable 5S concatameric arrays.
Biochemistry 2003, 42:4681-4690.
13. Hizume K, Yoshimura SH, Maruyama H, Kim J, Wada H,
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14. Lindstrom UM, Chandrasekaran RA, Orbai L, Helquist SA,
Miller GP, Oroudjev E, Hansma HG, Kool ET: Artificial human
telomeres from DNA nanocircle templates. Proc Natl Acad
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15. Oberleithner H, Schafer C, Shahin V, Albermann L: Route of
steroid-activated macromolecules through nuclear pores
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16. Sampaolese B, Bergia A, Scipioni A, Zuccheri G, Savino M,
Samori B, De Santis P: Recognition of the DNA sequence by
an inorganic crystal surface. Proc Natl Acad Sci USA 2002,
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17. Kornyshev AA, Leikin S: Electrostatic zipper motif for DNA
aggregation. Phys Rev Lett 1999, 82:4138-4141.
As a reviewer of Sitko’s paper [18], Leikin was so excited by the results
that he actually prepared samples and analyzed them by circular dichroism, revealing that GC-DNA had converted to Z-DNA in Ni(II), while
AT-DNA was still B-DNA.
18. Sitko JC, Mateescu EM, Hansma HG: Sequence-dependent DNA
condensation and the electrostatic zipper. Biophys J 2003,
84:419-431.
When the Hansma laboratory wanted to look at the unzipping of DNA
hairpins, as pioneered by the Gaub laboratory, they used a solution
containing Ni(II) to bind the DNA to mica; that was the origin of this
research.
19. Kato M, McAllister CJ, Hokabe S, Shimizu N, Lyubchenko YL:
Structural heterogeneity of pyrimidine/purine-biased DNA
sequence analyzed by atomic force microscopy.
Eur J Biochem 2002, 269:3632-3636.
20. Potaman VN, Bissler JJ, Hashem VI, Oussatcheva EA, Lu L,
Shlyakhtenko LS, Lyubchenko YL, Matsuura T, Ashizawa T,
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21. Dahlgren PR, Lyubchenko YL: Atomic force microscopy study of
the effects of Mg(2R) and other divalent cations on the end-toend DNA interactions. Biochemistry 2002, 41:11372-11378.
This paper has considerable data and lovely images of DNA molecules
that have joined end-to-end or circularized.
22. Shlyakhtenko LS, Miloseska L, Potaman VN, Sinden RR,
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Khalid S, Rodger PM, Peberdy JC, Isaac CJ, Rodger A et al.:
www.sciencedirect.com
Intramolecular DNA coiling mediated by metallosupramolecular cylinders: differential binding of P and M
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24. Rivetti C, Codeluppi S, Dieci G, Bustamante C: Visualizing RNA
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complexes of bacterial and eukaryotic RNA polymerases.
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27. Wang H, Yang Y, Schofield MJ, Du C, Fridman Y, Lee SD,
Larson ED, Drummond JT, Alani E, Hsieh P et al.: DNA bending
and unbending by MutS govern mismatch recognition and
specificity. Proc Natl Acad Sci USA 2003, 100:14822-14827.
28. Williams MC, Rouzina I: Force spectroscopy of single DNA and
RNA molecules. Curr Opin Struct Biol 2002, 12:330-336.
29. Bonin M, Zhu R, Klaue Y, Oberstrass J, Oesterschulze E, Nellen W:
Analysis of RNA flexibility by scanning force spectroscopy.
Nucleic Acids Res 2002, 30:e81.
The ‘pulls’ in this paper appear to be upside down, relative to the common
way of presenting forces and distances in force spectroscopy.
30. Krautbauer R, Pope LH, Schrader TE, Allen S, Gaub HE:
Discriminating small molecule DNA binding modes by single
molecule force spectroscopy. FEBS Lett 2002, 510:154-158.
Figure 1 in this paper has an excellent diagram of a classic DNA pulling
curve and the corresponding changes in the DNA molecule.
31. Albrecht C, Blank K, Lalic-Multhaler M, Hirler S, Mai T, Gilbert I,
Schiffmann S, Bayer T, Clausen-Schaumann H, Gaub HE:
DNA: a programmable force sensor. Science 2003, 301:367-370.
To quote Phil Szuromi of Science, this paper is ‘‘a forceful approach to
biological assays’’.
32. Bockelmann U: Single-molecule manipulation of nucleic acids.
Curr Opin Struct Biol 2004, 14:in press.
33. Jimenez-Ramirez J, Agredano-Moreno LT, Segura-Valdez ML,
Jimenez-Garcia LF: Lacandonia granules are present in
Ginkgo biloba cell nuclei. Biol Cell 2002, 94:511-518.
34. Adamcik J, Viglasky V, Valle F, Antalik M, Podhradsky D, Dietler G:
Effect of bacteria growth temperature on the distribution of
supercoiled DNA and its thermal stability. Electrophoresis 2002,
23:3300-3309.
35. Oh SJ, Cho SJ, Kim CO, Park JW: Characteristics of DNA
microarrays fabricated on various aminosilane layers.
Langmuir 2002, 18:1764-1769.
36. Kiselyova OI, Yaminsky IV, Karpova OV, Rodionova NP,
Kozlovsky SV, Arkhipenko MV, Atabekov JG: AFM study of
potato virus X disassembly induced by movement protein.
J Mol Biol 2003, 332:321-325.
This is a beautiful example of the use of AFM to answer a biochemical
question about the disassembly of a virus.
Current Opinion in Structural Biology 2004, 14:380–385