Cell Nucleic Acid Research Articles

Photoactivatable Blue Fluorescent Protein.

Photoactivatable and photoswitchable fluorescent proteins (FPs) are sophisticated molecular tools that in combination with super-resolution microscopy are helping to elucidate many biological processes. Through the Y66H mutation in the chromophore of the violet fluorescent protein SumireF, we created the first photoactivatable blue fluorescent protein (PA-BFP). This protein is rapidly activated over ordinary UV transilluminators at 302 or 365 nm in irreversible mode and by direct exposition to sunlight. The maximum excitation and emission wavelengths of this protein, centered at 358 and 445 nm, respectively, resemble the values of DAPI-the blue stain widely used in fluorescence microscopy to visualize nucleic acids in cells. Therefore, the immediate use of PA-BFP in cellular biology is clear because the technology required to follow this new genetically encoded reporter at the microscopic level has already been established. PA-BFP can potentially be used together with other photoactivatable fluorescent proteins of different colors to label multiple proteins, which can be simultaneously tracked by advanced microscopic techniques.

Nanocomposites consisting of titanium dioxide nanoparticles, antisense oligonucleotides, and photoactive groups as agents for effective action on nucleic acids

Relevance. Studies on model systems have confirmed the effectiveness of antisense oligonucleotides, including those that contain photoactive groups, for the modification of nucleic acids. However, this strategy has not yet found wide application due to the lack of successful methods for the cellular delivery. The development of effective preparations capable of acting on target nucleic acids in cells is an urgent task.
 The objective of the work is to create nanocomposites consisting of TiO2 nanoparticles, antisense oligonucleotides, and photoactive groups and to study their effect on target nucleic acids by the example of inhibition of influenza A virus replication in the cellular system.
 Materials and methods. Influenza virus A/Aichi/2/68 (A/H3N2), N-succinimide ether of p-azidotetrafluorobenzoic acid, TiO2 nanoparticles, and oligodeoxyribonucleotides have been used in the work. The antiviral activity of the proposed nanocomposites has been studied on the MDCK cells infected with the A/H3N2 virus.
 Results and discussion. Unique nanocomposites have been created, which consist of three functional components, i.e., titanium dioxide nanoparticles, antisense oligonucleotides, and the photoactive tetrafluoroarylazide group, respectively, providing penetration into cells, selective interaction with target nucleic acids, and photomodification of the targets. A significant antiviral site-specific action of the nanocomposites has been demonstrated against the influenza A virus in the cellular system, which exceeds the effect of the analogous samples that contain no photoactive groups.
 Conclusion. The biological activity of the created nanocomposites has been demonstrated by the example of highly effective suppression of influenza A virus replication in the cellular system. The results indicate the prospects of using the proposed drugs to affect target nucleic acids inside cells.

Harnessing single fluorescent probe to image deoxyribonucleic acid and ribonucleic acid in cells

The roles of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) in cells are closely related. However, the absence of molecular tools for simultaneous imaging of the two nucleic acids has prevented scientists from elucidating the regulatory mechanisms of nucleic acid interaction. The nucleic acid probes developed in recent years have ignored the regulatory relationship between DNA and RNA. Simultaneously imaging RNA and DNA in cells through a single small-molecule fluorescent probe is important. In this study, we propose a strategy for developing fluorescent probes localized to DNA and RNA to investigate their detection and imaging characteristics. The novel probe Bptp-RD has been successfully used for DNA and RNA imaging in cells. We investigated the detection and imaging characteristics of this nucleic acid probe and discovered the following: 1) the differences in the detection results of this nucleic acid probe for DNA and RNA come from the structural differences of the nucleic acids rather than chemical composition differences; 2) through using small-molecule probes to image a nucleic acid in cells, another nucleic acid can be visualized by reducing the fluorescence signal caused by DNA or RNA; 3) the order of response of the small-molecule fluorescent probe with intercalation and binding mechanisms to the type of nucleic acid structure is single chain, double chain, and ring. This work will help improve the understanding of RNA and DNA probes, and the novel probe has high potential to explore the interaction between RNA and DNA in cells.

Abstract 5631: Expanding tools for multiplex mRNA imaging in spatialomics through the ViewRNA tissue assay kits

Abstract Spatialomics is a rapidly growing field as it allows researchers to gain a deeper understanding of transcriptomes and corresponding protein expression profiles in cells within complex tissue microenvironments. One critical technology for spatialomics is in-situ hybridization (ISH) technology, which enables direct visualization and quantitation of nucleic acid in cells with single molecule resolution. The Invitrogen ViewRNA ISH assays incorporate branched DNA (bDNA) technology provides tools for interrogating multiple RNA transcripts at the same time, paving the way for improved spatialomics research. This technology is a powerful tool for spatialomics, giving insight into important mechanisms within cells and tissue. With researchers increasingly using spatialomic data in fields like neuroscience, immuno-oncology & single-cell analysis, these scientists will need the rapid and efficient detection of mRNA co-expression profiles that ViewRNA portfolio provides. In our newest offering, ViewRNA fluorescence tissue kits we extended our branched DNA technology, proprietary probe set design and signal amplification technology with Alexa Fluor probes offering a unique, robust, and sensitive in situ hybridization assay for RNA localization in fixed tissues. With fluorescence detection using Alexa Fluor 488, Alexa Fluor 546, Alexa Fluor 594, Alexa Fluor 647, and Alexa Fluor 750, these kits allow multiplexed detection and imaging paving the way for improved spatialomics. This technology lays the foundation for expanded fluorescent profiles to provide scientists additional tools to probe multiple transcripts per sample, allow broader spatialomics research. For Research Use Only. Not for use in diagnostic procedures. Citation Format: Nancie Mooney. Expanding tools for multiplex mRNA imaging in spatialomics through the ViewRNA tissue assay kits. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5631.

Study of complexation of single-stranded poly(rA) and poly(rU) with methylene blue

To reveal the effect of DNA- or RNA-specific low-molecular compounds on cellular processes on the molecular level, we have carried out the studies with the application of spectroscopic methods. It is necessary for the understanding of structural-functional properties of nucleic acids in cell. In this work the interaction of DNA-specific thiazine dye methylene blue (MB) with synthetic polynucleotides poly(rA) and poly(rU) was studied. The interaction of MB with synthetic polyribonucleotides poly(rA) and poly(rU) was examined in the solution with high ionic strength in a wide phosphate-to-dye (P/D) range, using the absorption and fluorescence spectroscopies, as well as the fluorescence 2D spectra and 3D spectra analyses were given. Values of the fluorescence quenching constants for the complexes of MB with poly(rA) and poly(rU) were calculated (KSV is the Stern-Volmer quenching constant). Two different modes of MB binding to single-stranded (ss-) poly(rA) and poly(rU) and to their hybrid double-stranded (ds-) structure – poly(rA)-poly(rU) were identified. This ligand binds to ss-poly(rA) and poly(rA)-poly(rU) by semi-intercalation and electrostatic modes, but to ss-poly(rU) the prevailing mode is the electrostatic interaction. Communicated by Ramaswamy H. Sarma

Progress in small-molecule fluorescent probes for nucleic acids

<p indent="0mm">Nucleic acids (NAs), including deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are biological macromolecular substances formed through the polymerization of nucleotide monomers. NAs contribute to the growth, development, and reproduction of living organisms. Due to developments in fluorescence-imaging technology, organic small-molecule fluorescent probes have become robust tools for imaging nucleic acid in cells, tissues, and <italic>in vivo</italic>. In this paper, based on the fluorophores, we systematically summarized the recent (2000–2021) progress in the development of organic small-molecule fluorescent probes for detecting NAs. In addition, the design strategies, reaction mechanisms, and biological applications of these fluorescent chemosensors were discussed in this review. Finally, the challenges and prospects of this promising field were discussed.

Thermodynamic Analysis to Elucidate the Behaviors of Nucleic Acids in Cells

Thermodynamic Analysis to Elucidate the Behaviors of Nucleic Acids in Cells

Dynamic queuosine changes in tRNA couple nutrient levels to codon choice in Trypanosoma brucei.

Every type of nucleic acid in cells undergoes programmed chemical post-transcriptional modification. Generally, modification enzymes use substrates derived from intracellular metabolism, one exception is queuine (q)/queuosine (Q), which eukaryotes obtain from their environment; made by bacteria and ultimately taken into eukaryotic cells via currently unknown transport systems. Here, we use a combination of molecular, cell biology and biophysical approaches to show that in Trypanosoma brucei tRNA Q levels change dynamically in response to concentration variations of a sub-set of amino acids in the growth media. Most significant were variations in tyrosine, which at low levels lead to increased Q content for all the natural tRNAs substrates of tRNA-guanine transglycosylase (TGT). Such increase results from longer nuclear dwell time aided by retrograde transport following cytoplasmic splicing. In turn high tyrosine levels lead to rapid decrease in Q content. Importantly, the dynamic changes in Q content of tRNAs have negligible effects on global translation or growth rate but, at least, in the case of tRNATyr it affected codon choice. These observations have implications for the occurrence of other tunable modifications important for ‘normal’ growth, while connecting the intracellular localization of modification enzymes, metabolites and tRNAs to codon selection and implicitly translational output.

Chemical Biology of Double Helical and Non-Double Helical Nucleic Acids: “To B or Not To B, That Is the Question”

Abstract Nucleic acids form not only the canonical double helix (duplex) but also the non-canonical (non-double helix) structures such as triplexes, G-quadruplexes, and i-motifs. The formation of these non-canonical structures and their stabilities depend on the microscopic environmental conditions around the nucleic acids. The intracellular environments, where various molecules are densely packed, exhibit molecular crowding. The non-canonical structures are very stable under molecular crowding conditions. The functions and structures of these nucleic acids in cells are optimized to enable them to function well in the crowded environments. We envisaged that molecular crowding in cells may play an important role in the reactions involving functionalized biomolecules and discovered a novel regulatory mechanism underlying the role of the non-canonical structures in gene expression. Based on the results of our work, we have developed novel methods to control the gene expression of non-double helical nucleic acids, leading to new insights into the chemistry of such nucleic acids. Our major achievements are summarized in this review.

Watson-Crick versus Hoogsteen Base Pairs: Chemical Strategy to Encode and Express Genetic Information in Life.

Nucleic acids typically form a double helix structure through Watson-Crick base-pairing. In contrast, non-Watson-Crick base pairs can form other three-dimensional structures. Although it is well-known that Watson-Crick base pairs may be more unstable than non-Watson-Crick base pairs under some conditions, the importance of non-Watson-Crick base pairs has not been widely examined. Hoogsteen base pairs, the non-Watson-Crick base pairs, contain important hydrogen-bond patterns that form the helices of nucleic acids, such as in Watson-Crick base pairs, and can form non-double helix structures such as triplexes and quadruplexes. In recent years, non-double helix structures have been discovered in cells and were reported to considerably influence gene expression. The complex behavior of these nucleic acids in cells is gradually being revealed, but the underlying mechanisms remain almost unknown.Quantitatively analyzing the structural stability of nucleic acids is important for understanding their behavior. A nucleic acid is an anionic biopolymer composed of a sugar, base, and phosphoric acid. The physicochemical factors that determine the stability of nucleic acid structures include those derived from the interactions of nucleic acid structures and those derived from the environments surrounding nucleic acids. The Gibbs free energy change (ΔG) of structure formation is the most commonly used physicochemical parameter for analyzing quantitative stability. Quantitatively understanding the intracellular behavior of nucleic acids involves describing the formation of nucleic acid structures and related reactions as ΔG. Based on this concept, we quantitatively analyzed the stability of double helix and non-double helix structures and found that decreased water activity, an important factor in crowded cellular conditions, significantly destabilize the formation of Watson-Crick base pairs but stabilizes Hoogsteen base pairs.Here, we describe a physicochemical approach to understand the regulation of gene expressions based on the stability of nucleic acid structures. We developed new methods for predicting the stability of double and non-double helices in various molecular environments by mimicking intracellular environments. Furthermore, the physicochemical approach used for analyzing gene expression regulated by non-double helix structures is useful for not only determining how gene expression is controlled by cellular environments but also for developing new technologies to chemically regulate gene expression by targeting non-double helix structures. We discuss the roles of Watson-Crick and Hoogsteen base pairs in cells based on our results and why both types of base pairing are required for life. Finally, a new concept in nucleic acid science beyond that of Watson and Crick base pairing is introduced.

DNA/RNA Fluorescence Imaging by Synthetic Nucleic Acids.

Fluorescence imaging of nucleic acids is a key technology needed to understand gene expression and the resulting changes in cellular function. This chapter focuses on sequence-specific fluorescence imaging of nucleic acids in cells using fluorescent nucleic acids. The design and preparation of fluorescent nucleic acids and their application to fluorescence imaging of intracellular nucleic acids are introduced.

Simul‐staining manganese oxides and microbial cells

AbstractManganese oxide minerals (Mn(III/IV)Ox) are ubiquitous in natural environments and interactions between Mn(III/IV)Ox and microbes play important roles in biogeochemical cycles. Current techniques for determining the spatial distribution of microbes with Mn(III/IV)Ox include electron microscopy and synchrotron radiation analyses. However, these techniques may not be readily available in most laboratories or may be cost prohibitive. Here we present a rapid, cost‐effective “simul‐staining” method for imaging particulate Mn(III/IV)Ox and cells on the same filter using epifluorescence microscopy with differential interference contrast (DIC) capability as a prescreening tool before higher resolution and/or more time‐intensive analyses. This method uses leucoberbelin blue (LBB) dye, which turns blue when oxidized by particulate Mn(III/IV)Ox on filters, and the fluorescent nucleic acid stain, SYBR Green, which fluoresces when bound to nucleic acids. First, the DIC configuration is used to locate blue “haloes” of oxidized LBB around Mn(III/IV)Ox particles. Second, a filter set that excites dyes with blue light and emits green fluorescence is used to image SYBR Green bound to nucleic acids in cells. Third, ImageJ is used for image analysis to associate Mn(III/IV)Ox particles and microbes. We demonstrate that this simul‐staining is suitable for laboratory cultures of manganese‐oxidizing bacteria as well as environmental samples from a marine oxycline.

Global profile changes in transcripts induced with a phosphate analogue: implications for gene regulation.

Previous work has shown that thiophosphate, a phosphate analogue, leads to a global shift in the distribution of cellular proteins in a variety of organisms. Thiophosphate, when added to culture media, gets incorporated into the nucleic acids of cells resulting in nuclease-resistant phosphorothioate linkages. Using Escherichia coli, as a model organism, it was found that the global changes in protein expression induced with thiophosphate could be accounted for by significant changes in the absolute transcription levels of more than 1500 genes detected via RNA seq analysis. In fact, 58% of transcripts detected in RNA seq studies using total RNA were increased an average of 44 × fold while the remaining 42% were decreased an average of 20 × fold in thiophosphate-treated cells. Furthermore, microarray results showed no correlation between the transcriptional changes observed and the known stability of the corresponding mRNAs measured. Overall, the total amount of non-ribosomal RNA accumulated in TP-treated cells was increased relative to rRNA ~ 4 × fold (1.5-6 ×). The results further indicated that metabolic changes may play a role in inducing the transcriptional profiles observed with thiophosphate. Indeed, pathway analysis of transcripts showed an increase in routes for phosphoribosyl pyrophosphate (PRPP) synthesis and related derivatives, presumably due to a reduction in RNA turnover. These results raise the possibility that the energy savings with reduced RNA turnover could lead to an increased energy charge in the cell that induces transcriptional changes leading to an increase in biosynthetic processes.

Tracking nucleic acids in living cells

Biotechnology Fluorescence in situ hybridization (FISH) is a powerful molecular technique for detecting nucleic acids in cells. However, it requires cell fixation and denaturation. Wang et al. found that CRISPR-Cas9 protects guide RNAs from degradation in cells only when bound to target DNA. Taking advantage of this target-dependent stability switch, they developed a labeling technique, named CRISPR LiveFISH, to detect DNA and RNA using fluorophore-conjugated guide RNAs with Cas9 and Cas13, respectively. CRISPR LiveFISH improves the signal-to-noise ratio, is compatible with living cells, and allows tracking real-time dynamics of genome editing, chromosome translocation, and transcription. Science , this issue p. [1301][1] [1]: /lookup/doi/10.1126/science.aax7852

A new method for diagnosing biochemical abnormalities of anterior cruciate ligament (ACL) in human knees: A Raman spectroscopic study

Anterior cruciate ligament (ACL) plays an essential role in knee joint stability and kinematics. The microstructural irregularities such as cellular changes and disorganization of the extracellular matrix (ECM) alter the mechanical properties of the ligament, leading to a significant knee functional instability and progression of osteoarthritis (OA). So far, the identification of the local abnormality in ACL has routinely relied on invasive analytical techniques such as histology or biochemical assays. The non-invasive diagnosis using magnetic resonance imaging (MRI) is still limited to identifying the presence/absence of partial/complete ruptures and mucoid degeneration. In this study, laser micro-Raman spectroscopy with near-infrared excitation (785 nm) was applied to human ACL in order to establish optical algorithms for non-destructively diagnosing a degeneration state at molecular level.Raman spectra were obtained from 44 ex-vivo ACL specimens, and these were subsequently classified as an early (subclinical) and advanced (clinical) level of tissue degradation based on the histopathological scoring system. The significant differences in Raman peak intensities were found between the different degeneration groups, which were assigned to the vibrational modes of nucleic acids in cells, collagens, and phospholipids. Linear discriminant analysis (LDA) was performed to identify cut-off values for the distributions of Raman intensity and intensity ratios, which enable to best discriminate between the early and advanced degenerated tissues. Raman intensity algorithms derived from I1101/I1749, [I1002/I1516vs. I1101/I1749], and [I1002/I1749vs. I1101/I1749], yielded a maximum diagnostic sensitivity of 100%, specificity of 80%, and accuracy of 91% for discriminating the degeneration severity. Statement of SignificanceIn this study, laser micro-Raman spectroscopy was applied to human anterior cruciate ligament (ACL) to establish optical algorithms for non-destructively diagnosing the tissue degeneration at molecular level. To our knowledge, this is the first report on Raman diagnosis for human ACL. Linear discriminant analysis (LDA) was performed to identify cut-off values for Raman intensity and intensity ratios, which enable to best discriminate between an early (subclinical) and advanced (clinical) level of ACL degeneration. The intensity ratios of I1101/I1749, [I1002/I1516vs. I1101/I1749], and [I1002/I1749vs. I1101/I1749] yielded a maximum diagnostic sensitivity of 100%, specificity of 80%, and accuracy of 91% for discriminating the ACL degeneration. The present findings might contribute to expanding clinical diagnostic possibilities for non-invasively identifying tissue degeneration.

CRISPR-mediated live imaging of genome editing and transcription.

We report a robust, versatile approach called CRISPR live-cell fluorescent in situ hybridization (LiveFISH) using fluorescent oligonucleotides for genome tracking in a broad range of cell types, including primary cells. An intrinsic stability switch of CRISPR guide RNAs enables LiveFISH to accurately detect chromosomal disorders such as Patau syndrome in prenatal amniotic fluid cells and track multiple loci in human T lymphocytes. In addition, LiveFISH tracks the real-time movement of DNA double-strand breaks induced by CRISPR-Cas9-mediated editing and consequent chromosome translocations. Finally, by combining Cas9 and Cas13 systems, LiveFISH allows for simultaneous visualization of genomic DNA and RNA transcripts in living cells. The LiveFISH approach enables real-time live imaging of DNA and RNA during genome editing, transcription, and rearrangements in single cells.

Application of ion pair chromatography coupled with mass spectrometry to assess antisense oligonucleotides concentrations in living cells.

Antisense oligonucleotides (ASOs) are synthetic bioactive compounds used as therapeutic agents in clinical trials. They act by binding to complementary sequences of the targeted nucleic acids in cells. Assessing the efficiency of ASO delivery to cells or tissues and the stability of these compounds in different biological systems is important. To answer these questions, we developed a new, quick and reliable method to determine the concentrations of different types of ASOs in treated cells. Ultra-high performance liquid chromatography coupled with mass spectrometry was used for the first time for the separation and determination of the studied compounds in total RNA extracts. To develop a method with the highest possible sensitivity, a central composite design was used to comprehensively optimize the MS parameters. Moreover, the effects of the type and concentration of the ion pair reagent on sensitivity were also examined. Finally, a mobile phase containing methanol, hexafluoroisopropanol and N,N-dimethylbutylamine was selected. The optimized method allowed good linearity, accuracy, precision and sensitivity of ASO detection. Next, these compounds were delivered into cells via transfection at a concentration of 25 nM or 125 nM in 1 mL of cell culture medium. After 48 hours, total RNA was isolated from the treated cells and analyzed with the use of the newly developed method. For the cells treated with a higher concentration of ASO composed of phosphorothioate 2'-O-methyl RNA units, the concentration in solution was 0.96 ± 0.06 μM, while in the case of shorter ASO composed of locked nucleic acid units, it was 0.72 ± 0.06 μM in the total RNA extract.

ClampFISH detects individual nucleic acid molecules using click chemistry-based amplification.

Methods for detecting single nucleic acids in cell and tissues, such as fluorescence in situ hybridization (FISH), are limited by relatively low signal intensity and non-specific probe binding. Here we present click-amplifying FISH (clampFISH), a method for fluorescence detection of nucleic acids that achieves high specificity and high-gain (>400x) signal amplification. ClampFISH probes form a “C” configuration upon hybridization to the sequence of interest in a double helical manner. The ends of the probes are ligated together using bioorthogonal click chemistry, effectively locking the probes around the target. Iterative rounds of hybridization and click amplify the fluorescence intensity. We show that clampFISH enables the detection of RNA species with low magnification microscopy and in RNA-based flow cytometry. Additionally, we show that the modular design of clampFISH probes allows multiplexing of RNA and DNA detection, that the locking mechanism prevents probe detachment in expansion microscopy, and that clampFISH can be applied in tissue samples.

Talk title Bridging the gap between RNA editing and modification: A 10‐year solution to a 25‐year problem

All types of nucleic acids in cells undergo naturally occurring chemical modifications, including DNA, rRNA, mRNA, snRNA, and most prominently tRNA. Over 100 different modifications have been described and every position in the purine and pyrimidine bases has been seen modified; the sugar is often also modified. Despite recent progress, the mechanism for the synthesis of most modifications is not fully understood partly due to difficulty in reconstituting modification enzyme activity in vitro. Cytosine to uridine (C to U) editing of tRNAs in eukaryotes was first discovered over 20 years ago, yet due to the lack of an in vitro assay, the editing enzyme is still at large and the editing mechanism remains unsolved. In this work we show that cytosine 32 in the anticodon loop of tRNAThr is methylated to 3‐methylcytosine (m3C) as a pre‐requisite for C to U deamination. Formation of m3C in vitro requires the presence of both TbTRM140 (the m3C methyltransferase) and the TbADAT2/3 (the A to I editing deaminase). Once m3C is formed the same set of enzymes are required for further deamination from m3C to form 3‐methyluridine (m3U). In our previous work, we also showed that TbADAT2/3 was a highly mutagenic enzyme randomly deaminating DNA. Now we provide evidence that when co‐expressed with the methylase its mutagenic ability is kept in check via complex formation with TRM140. This helps explain how T. brucei escapes “wholesale deamination” of its genome while harboring both enzymes in its nuclear compartment. This observation has implications for the control of another mutagenic deaminase, human AID, and provides a rationale for its regulation.Support or Funding InformationNIH GM084065This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Peptide-Based Probes with an Artificial Anion-Binding Motif for Direct Fluorescence "Switch-On" Detection of Nucleic Acid in Cells.

This work reports two new peptide-based fluorescence probes (1 and 2) for the detection of ds-DNA at physiological pH. Probes 1 and 2 contain a fluorophore, either amino-naphthalimide or diethyl-aminocoumarin, respectively, and two identical peptide arms each equipped with a guanidiniocarbonylpyrrole (GCP) anion-binding motif. These probes show "switch-on" fluorescence response upon binding to ds-DNA, whereby they can differentiate between various types of polynucleotides. For instance, they exhibit more pronounced fluorescence response for AT-rich polynucleotides than GC-rich polynucleotides, and both give only negligible response to ds-RNA. The fluorimetric response of 1 is proportional to the AT-basepair content in DNA, whereas the fluorescence of 2 is sensitive to the secondary structure of the polynucleotide. Fluorescence experiments, thermal melting experiments and circular dichroism studies suggest that 1 interacts with ds-DNA in a combined intercalation and minor groove binding, whereas 2 interacts mainly with the outer surface of DNA/RNA. As 1 and 2 have a very low cytotoxicity, 1 can be applied for the imaging of nuclear DNA in cells.