Diaminopurine Research Articles

The selective chemical modification of the 6-amino group of adenosine of the premature termination codon induces readthrough to produce full-length peptide in the reconstituted E. Coli translation system

Nonsense mutations in the coding region turn amino acid codons into termination codons, resulting in premature termination codons (PTCs). In the case of the in-frame PTC, if translation does not stop at the PTC but continues to the natural termination codon (NTC) with the insertion of an amino acid, known as readthrough, the full-length peptide is formed, albeit with a single amino acid mutation. We have previously developed the functionality-transfer oligonucleotide (FT-Probe), which forms a hybrid complex with RNA of a complementary sequence to transfer the functional group, resulting in modification of the 4-amino group of cytosine or the 6-amino group of adenine. In this study, the FT-Probe was used to chemically modify the adenosines of the PTC (UAA, UAG, and UGA) of mRNA, which were assayed for the readthrough in a reconstituted Escherichia coli translation system. The third adenosine-modified UAA produced three readthrough peptides incorporating tyrosine, glutamine and lysine at the UAA site. It should be noted that the additional modification with a cyclodextrin only induced glutamine incorporation. The adenosine modified UGA induced readthrough very efficiently with selective tryptophan incorporation. Readthrough of the modified UGA is caused by inhibition of the RF2 function. This study has demonstrated that the chemical modification of the adenosine 6-amino group of the PTC is a strategy for effective readthrough in a prokaryotic translation system.

Crystal structures of pertussis toxin with NAD+ and analogs provide structural insights into the mechanism of its cytosolic ADP-ribosylation activity

Bordetella pertussis is the causative agent of whooping cough, a highly contagious respiratory disease. Pertussis toxin (PT), a major virulence factor secreted by B. pertussis, is an AB5-type protein complex topologically related to cholera toxin. The PT protein complex is internalized by host cells and follows a retrograde trafficking route to the endoplasmic reticulum, where it subsequently dissociates. The released enzymatic S1 subunit is then translocated from the endoplasmic reticulum into the cytosol and subsequently ADP-ribosylates the inhibitory alpha-subunits (Gαi) of heterotrimeric G proteins, thus promoting dysregulation of G protein–coupled receptor signaling. However, the mechanistic details of the ADP-ribosylation activity of PT are not well understood. Here, we describe crystal structures of the S1 subunit in complex with nicotinamide adenine dinucleotide (NAD+), with NAD+ hydrolysis products ADP-ribose and nicotinamide, with NAD+ analog PJ34, and with a novel NAD+ analog formed upon S1 subunit crystallization with 3-amino benzamide and NAD+, which we name benzamide amino adenine dinucleotide. These crystal structures provide unprecedented insights into pre- and post-NAD+ hydrolysis steps of the ADP-ribosyltransferase activity of PT. We propose that these data may aid in rational drug design approaches and further development of PT-specific small-molecule inhibitors.

Nanomechanics of negatively supercoiled diaminopurine-substituted DNA

Single molecule experiments have demonstrated a progressive transition from a B- to an L-form helix as DNA is gently stretched and progressively unwound. Since the particular sequence of a DNA segment influences both base stacking and hydrogen bonding, the conformational dynamics of B-to-L transitions should be tunable. To test this idea, DNA with diaminopurine (DAP) replacing adenine was synthesized to produce linear fragments with triply hydrogen-bonded DAP:T base pairs. Triple hydrogen bonding stiffened the DNA by 30% flexurally.

Nanomechanics of negatively supercoiled diaminopurine-substituted DNA.

Single molecule experiments have demonstrated a progressive transition from a B- to an L-form helix as DNA is gently stretched and progressively unwound. The particular sequence of a DNA segment defines both base stacking and hydrogen bonding that affect the partitioning and conformations of the two phases. Naturally or artificially modified bases alter H-bonds and base stacking and DNA with diaminopurine (DAP) replacing adenine was synthesized to produce linear fragments with triply hydrogen-bonded DAP:T base pairs. Both unmodified and DAP-substituted DNA transitioned from a B- to an L-helix under physiological conditions of mild tension and unwinding. This transition avoids writhing and the ease of this transition may prevent cumbersome topological rearrangements in genomic DNA that would require topoisomerase activity to resolve. L-DNA displayed about tenfold lower persistence length than B-DNA. However, left-handed DAP-substituted DNA was twice as stiff as unmodified L-DNA. Unmodified DNA and DAP-substituted DNA have very distinct mechanical characteristics at physiological levels of negative supercoiling and tension.

Effect of the Solvent and Substituent on Tautomeric Preferences of Amine-Adenine Tautomers.

Adenine is one of the basic molecules of life; it is also an important building block in the synthesis of new pharmaceuticals, electrochemical (bio)sensors, or self-assembling molecular materials. Therefore, it is important to know the effects of the solvent and substituent on the electronic structure of adenine tautomers and their stability. The four most stable adenine amino tautomers (9H, 7H, 3H, and 1H), modified by substitution (C2– or C8−) of electron-withdrawing NO2 and electron-donating NH2 groups, are studied theoretically in the gas phase and in solvents of different polarities (1 ≤ ε < 109). Solvents have been modeled using the polarizable continuum model. Comparison of the stability of substituted adenine tautomers in various solvents shows that substitution can change tautomeric preferences with respect to the unsubstituted adenine. Moreover, C8 substitution results in slight energy differences between tautomers in polar solvents (<1 kcal/mol), which suggests that in aqueous solution, C8–X-substituted adenine systems may consist of a considerable amount of two tautomers—9H and 7H for X = NH2 and 3H and 9H for X = NO2. Furthermore, solvation enhances the effect of the nitro group; however, the enhancement strongly depends on the proximity effects. This enhancement for the NO2 group with two repulsive N···ON contacts can be threefold higher than that for the NO2 with one attractive NH···ON contact. The proximity effects are even more significant for the NH2 group, as the solvation may increase or decrease its electron-donating ability, depending on the type of proximity.

Site-Specific Photo-oxidation of the Isolated Adenosine-5'-triphosphate Dianion Determined by Photoelectron Imaging.

Photoelectron imaging of the isolated adenosine-5'-triphosphate dianion excited to the 1ππ* states reveals that electron emission is predominantly parallel to the polarization axis of the light and arises from subpicosecond electron tunneling through the repulsive Coulomb barrier (RCB). The computed RCB shows that the most probable electron emission site is on the amino group of adenine. This is consistent with the photoelectron imaging: excitation to the 1ππ* states leads to an aligned ensemble distributed predominantly parallel to the long axis of adenine; the subsequent electron tunneling site is along this axis; and the negatively charged phosphate groups guide the outgoing electron mostly along this axis at long range. Imaging of electron tunneling from polyanions combined with computational chemistry may offer a general route for probing the intrinsic photo-oxidation site and dynamics as well as the overall structure of complex isolated species.

Beta class amino methyltransferases from bacteria to humans: evolution and structural consequences.

S-adenosyl-l-methionine dependent methyltransferases catalyze methyl transfers onto a wide variety of target molecules, including DNA and RNA. We discuss a family of methyltransferases, those that act on the amino groups of adenine or cytosine in DNA, have conserved motifs in a particular order in their amino acid sequence, and are referred to as class beta MTases. Members of this class include M.EcoGII and M.EcoP15I from Escherichia coli, Caulobacter crescentus cell cycle–regulated DNA methyltransferase (CcrM), the MTA1-MTA9 complex from the ciliate Oxytricha, and the mammalian MettL3-MettL14 complex. These methyltransferases all generate N6-methyladenine in DNA, with some members having activity on single-stranded DNA as well as RNA. The beta class of methyltransferases has a unique multimeric feature, forming either homo- or hetero-dimers, allowing the enzyme to use division of labor between two subunits in terms of substrate recognition and methylation. We suggest that M.EcoGII may represent an ancestral form of these enzymes, as its activity is independent of the nucleic acid type (RNA or DNA), its strandedness (single or double), and its sequence (aside from the target adenine).

Impact of the Substituents on the Electronic Structure of the Four Most Stable Tautomers of Purine and Their Adenine Analogues.

Substituent effects at the C2-, C8-, and N-positions of adenine and purine on the structural and π-electronic changes in their four tautomers were studied using the B97D3/aug-cc-pvdz computational level. The effect of various substituents (NO2, CN, CHO, Cl, F, H, Me, OMe, OH, and NH2) was characterized by the charge of the substituent active region (cSAR) approach and Hammett substituent constants σ. It has been found that for both adenine and purine derivatives, substituents from the C8–X position have a stronger influence on their electronic structure than from the C2–X and N–X positions. The presence of the amino group in adenine enhances the substituent effect compared to that which occurs in purine. In addition, its electronic structure is more sensitive to the effect of the substituent in 3H and 1H than in the 9H and 7H adenine tautomers. For a given substituent, a large variation in cSAR(X) values is observed, strongly dependent on the substitution position. For 7H and 9H adenine tautomers for C8–X systems, substituents reduce the aromaticity of the five-membered rings but increase the aromaticity of the six-membered rings.

Factors that control the gold nanoparticles' aggregation induced by adenine molecules: New insights through a combined experimental and theoretical study

The adsorption of adenine molecules and its derivatives on citrate capped gold nanoparticles (AuNPs) is quantified by a colorimetric method. The strength of the interaction is reflected in the aggregation grade of the colloids, that is detected though the changes in the absorption spectra of the samples, which allow for the determination of apparent binding constants. The positive charge of adenine molecules facilitates the approach to the colloid surface, a fact that is reflected in the measured binding free energies being more negative than those of neutral molecules. In the case of nucleosides and nucleotides, the aggregated structures are smaller or simply do not appear. Theoretical calculations based on density functional theory (DFT) were performed in order to compare the interaction of adenine, adenosine and AMP with gold nanoparticles. Our results indicate the relevance of the N atom of the amino group of adenine, adenosine and AMP in the stabilization with the nanoparticle surface. Thus, in this stabilization the amino group adopts a pyramidal disposition typical of a sp3 hybridization, being found the gold-adenine interaction more stable than that of adenosine and AMP.

ATP Mimics pH-Dependent Dual Peroxidase-Catalase Activities Driving H 2 O 2 Decomposition

Adenosine triphosphate (ATP) is produced mainly in the mitochondrion, and its primary task is to function as a ubiquitous energy currency to meet the cellular metabolic demands in biological system...

Dependence of Leishmania parasite on host derived ATP: an overview of extracellular nucleotide metabolism in parasite.

The widespread role of ATP in humans has been characterized as a substrate for metabolism as well as other key processes occurring in the human system. Hence, the ATP pool may also be accessible to the invaders, including Leishmania donovani (a protozoan parasite), considering the fact that ATP is not scarce at the cellular location where the pathogen resides. The protozoan parasite survives in the human host by utilizing purines from its extracellular environment, due to its inability to synthesize purines de novo. The purines are accessible in the form of nucleoside triphosphates (NTPs), for example, adenosine (ADO) in the form of ATP molecules. These NTPs are processed by the ecto-nucleotidases in the transmembrane region of the parasite, which are then transported inside via nucleoside/nucleobase transporters belonging to the ENT family of transporters. Besides, the breakdown of NTPs by ecto-nucleotidases also yields inorganic phosphate (Pi) as by-product which is utilized by the parasite to maintain Pi homeostasis. These transporters have been characterized in protozoan parasites exhibiting homology in various species of Leishmania. Once inside the parasite, these purines (or their derivatives) are fluxed into purine metabolic pathways with the help of several cytosolic enzymes, prominently, adenosine deaminase, adenine amino hydrolase, phosphoribosyl transferases (APRT, HGPRT and XPRT) and adenosine kinase. This review outlines the predominant role of extracellular nucleotide metabolism and intracellular metabolic machinery in the containment of leishmanial infection. It also highlights the importance of inorganic phosphate transporter in relation to the purine transport.

Mechanisms of the action of adenine on anti-allergic effects in mast cells.

IntroductionMast cells play an important role in allergic responses.MethodsWe herein demonstrated the mechanisms of inhibitory effect of adenine on IgE/antigen‐induced degranulation and TNF‐α release in mast cells.ResultsWe found that these effects were dependent on the amino group of adenine because purine only weakly inhibited degranulation. Adenine also inhibited Ca2+ ionophore‐ and thapsigargin‐induced degranulation, however, this inhibitory effect was weaker than that of the antigen. Therefore, the inhibitory effects of adenine on degranulation may be mediated before as well as after the Ca2+ raise under the antigen stimulus. Adenine inhibited antigen‐induced Syk and the subsequent induction of AKT and ERK activation under FcϵRI‐mediated signal. Adenine also attenuated antigen‐induced increase in Ca2+. Furthermore, adenine inhibited IgE/antigen‐induced IKKα/β activation, which is involved in degranulation. Finally, adenine protected mice against anaphylactic allergic responses in vivo.ConclusionsThe present study revealed a key role of adenine in the attenuation of allergic responses through the inhibition of Syk‐mediated signal transduction and IKK‐mediated degranulation.

Vibrational fingerprints of N6-methyladenine and N6,N6-dimethyladenine in Raman spectra

Vibrational fingerprints of N6-methyladenine (NMA) and N6,N6-dimethyladenine (NDMA) on gold nanoparticles (AuNPs) were investigated by means of Raman spectroscopy. NMA and NDMA have one methyl group and two methyl groups, respectively, at the amino moiety of the adenine purine unit. Surface-enhanced Raman scattering (SERS) spectra were analyzed to explain the difference in the spectral features among adenine, NMA, and NDMA based on density functional theory (DFT) calculations on gold clusters. NMA has unique bands at 717 and 1101cm−1 in their SERS spectra on AuNPs, which can be differentiated from those of adenine. After observing these unique spectra features, the SERS spectra of NMA and NDMA on AuNPs were dissimilar, suggesting that the methyl group at the amino groups of the adenine may be significantly affecting the binding on AuNPs, as supported by DFT calculations of NMA and NDMA on gold clusters. Our Raman study indicates that the methylation at the amino group in adenine may play a significant role in providing vibrational finger prints in the SERS spectra on metal surfaces.

E. Coli Gyrase Fails to Negatively Supercoil Diaminopurine-Substituted DNA

Type II topoisomerases modify DNA supercoiling, and crystal structures suggest that they sharply bend the gate segment DNA in the process. Bacterial gyrases are a class of type II topoisomerases which introduce negative supercoiling by also tightly wrapping DNA flanking the gate segment before strand passage. To reveal whether topoisomerases can bend or wrap artificially stiffened DNA, E. coli gyrase and human topoisomerase IIα were challenged with normal DNA or stiffer DNA produced by PCR reactions in which diaminopurine (DAP) replaced adenine deoxyribonucleotidetriphosphates. The rates or pauses during relaxation of positive supercoils produced with magnetic tweezers in single molecules of DAP-substituted versus normal DNA distinguished the enzymes. Gyrase struggled to bend or perhaps open a gap in DAP-substituted DNA, and segments of wider DAP DNA may have fit poorly into the N-gate of the human topoisomerase IIα. Pauses during processive activity on both types of DNA exhibited ATP-dependence consistent with two pathways leading to the strand-passage competent state with a bent gate segment and a transfer segment trapped by an ATP-loaded and latched N-gate. However, E. coli DNA gyrase did not negatively supercoil 35% stiffer DAP DNA most likely by failing to wrap DNA flanking the gate segment before strand passage.

A 7-Deazaadenosylaziridine Cofactor for Sequence-Specific Labeling of DNA by the DNA Cytosine-C5 Methyltransferase M.HhaI.

DNA methyltransferases (MTases) catalyze the transfer of the activated methyl group of the cofactor S-adenosyl-l-methionine (AdoMet or SAM) to the exocyclic amino groups of adenine or cytosine or the C5 ring atom of cytosine within specific DNA sequences. The DNA adenine-N6 MTase from Thermus aquaticus (M.TaqI) is also capable of coupling synthetic N-adenosylaziridine cofactor analogues to its target adenine within the double-stranded 5′-TCGA-3′ sequence. This M.TaqI-mediated coupling reaction was exploited to sequence-specifically deliver fluorophores and biotin to DNA using N-adenosylaziridine derivatives carrying reporter groups at the 8-position of the adenine ring. However, these 8-modified aziridine cofactors were poor substrates for the DNA cytosine-C5 MTase from Haemophilus haemolyticus (M.HhaI). Based on the crystal structure of M.HhaI in complex with a duplex oligodeoxynucleotide and the cofactor product, we synthesized a stable 7-deazaadenosylaziridine derivative with a biotin group attached to the 7-position via a flexible linker. This 7-modified aziridine cofactor can be efficiently used by M.HhaI for the direct, quantitative and sequence-specific delivery of biotin to the second cytosine within 5′-GCGC-3′ sequences in short duplex oligodeoxynucleotides and plasmid DNA. In addition, we demonstrate that biotinylation by M.HhaI depends on the methylation status of the target cytosine and, thus, could provide a method for cytosine-C5 DNA methylation detection in mammalian DNA.

The m1A58 modification in eubacterial tRNA: An overview of tRNA recognition and mechanism of catalysis by TrmI

The enzymes of the TrmI family catalyze the formation of the m1A58 modification in tRNA. We previously solved the crystal structure of the Thermus thermophilus enzyme and conducted a biophysical study to characterize the interaction between TrmI and tRNA. TrmI enzymes are active as a tetramer and up to two tRNAs can bind to TrmI simultaneously. In this paper, we present the structures of two TrmI mutants (D170A and Y78A). These residues are conserved in the active site of TrmIs and their mutations result in a dramatic alteration of TrmI activity. Both structures of TrmI mutants revealed the flexibility of the N-terminal domain that is probably important to bind tRNA. The structure of TrmI Y78A catalytic domain is unmodified regarding the binding of the SAM co-factor and the conformation of residues potentially interacting with the substrate adenine. This structure reinforces the previously proposed role of Y78, i.e. stabilize the conformation of the A58 ribose needed to hold the adenosine in the active site. The structure of the D170A mutant shows a flexible active site with one loop occupying in part the place of the co-factor and the second loop moving at the entrance to the active site. This structure and recent data confirms the central role of D170 residue binding the amino moiety of SAM and the exocyclic amino group of adenine. Possible mechanisms for methyl transfer are then discussed.

DNA-Protein Cross-Links: Formation, Structural Identities, and Biological Outcomes.

Noncovalent DNA-protein interactions are at the heart of normal cell function. In eukaryotic cells, genomic DNA is wrapped around histone octamers to allow for chromosomal packaging in the nucleus. Binding of regulatory protein factors to DNA directs replication, controls transcription, and mediates cellular responses to DNA damage. Because of their fundamental significance in all cellular processes involving DNA, dynamic DNA-protein interactions are required for cell survival, and their disruption is likely to have serious biological consequences. DNA-protein cross-links (DPCs) form when cellular proteins become covalently trapped on DNA strands upon exposure to various endogenous, environmental and chemotherapeutic agents. DPCs progressively accumulate in the brain and heart tissues as a result of endogenous exposure to reactive oxygen species and lipid peroxidation products, as well as normal cellular metabolism. A range of structurally diverse DPCs are found following treatment with chemotherapeutic drugs, transition metal ions, and metabolically activated carcinogens. Because of their considerable size and their helix-distorting nature, DPCs interfere with the progression of replication and transcription machineries and hence hamper the faithful expression of genetic information, potentially contributing to mutagenesis and carcinogenesis. Mass spectrometry-based studies have identified hundreds of proteins that can become cross-linked to nuclear DNA in the presence of reactive oxygen species, carcinogen metabolites, and antitumor drugs. While many of these proteins including histones, transcription factors, and repair proteins are known DNA binding partners, other gene products with no documented affinity for DNA also participate in DPC formation. Furthermore, multiple sites within DNA can be targeted for cross-linking including the N7 of guanine, the C-5 methyl group of thymine, and the exocyclic amino groups of guanine, cytosine, and adenine. This structural complexity complicates structural and biological studies of DPC lesions. Two general strategies have been developed for creating DNA strands containing structurally defined, site-specific DPCs. Enzymatic methodologies that trap DNA modifying proteins on their DNA substrate are site specific and efficient, but do not allow for systematic studies of DPC lesion structure on their biological outcomes. Synthetic methodologies for DPC formation are based on solid phase synthesis of oligonucleotide strands containing protein-reactive unnatural DNA bases. The latter approach allows for a wider range of protein substrates to be conjugated to DNA and affords a greater flexibility for the attachment sites within DNA. In this Account, we outline the chemistry of DPC formation in cells, describe our recent efforts to identify the cross-linked proteins by mass spectrometry, and discuss various methodologies for preparing DNA strands containing structurally defined, site specific DPC lesions. Polymerase bypass experiments conducted with model DPCs indicate that the biological outcomes of these bulky lesions are strongly dependent on the peptide/protein size and the exact cross-linking site within DNA. Future studies are needed to elucidate the mechanisms of DPC repair and their biological outcomes in living cells.

E. coli Gyrase Fails to Negatively Supercoil Diaminopurine-Substituted DNA

Type II topoisomerases modify DNA supercoiling, and crystal structures suggest that they sharply bend DNA in the process. Bacterial gyrases are a class of type II topoisomerases that can introduce negative supercoiling by creating a wrap of DNA before strand passage. Isoforms of these essential enzymes were compared to reveal whether they can bend or wrap artificially stiffened DNA. Escherichia coli gyrase and human topoisomerase IIα were challenged with normal DNA or stiffer DNA produced by polymerase chain reaction reactions in which diaminopurine (DAP) replaced adenine deoxyribonucleotide triphosphates. On single DNA molecules twisted with magnetic tweezers to create plectonemes, the rates or pauses during relaxation of positive supercoils in DAP-substituted versus normal DNA were distinct for both enzymes. Gyrase struggled to bend or perhaps open a gap in DAP-substituted DNA, and segments of wider DAP DNA may have fit poorly into the N-gate of the human topoisomerase IIα. Pauses during processive activity on both types of DNA exhibited ATP dependence consistent with two pathways leading to the strand-passage-competent state with a bent gate segment and a transfer segment trapped by an ATP-loaded and latched N-gate. However, E. coli DNA gyrase essentially failed to negatively supercoil 35% stiffer DAP DNA.

Connectivity patterns and rotamer states of nucleobases determine acid–base properties of metalated purine quartets

Potentiometric pH titrations and pD dependent 1H NMR spectroscopy have been applied to study the acidification of the exocyclic amino group of adenine (A) model nucleobases (N9 position blocked by alkyl groups) when carrying trans-a2PtII (with a=NH3 or CH3NH2) entities both at N1 and N7 positions. As demonstrated, in trinuclear complexes containing central A–Pt–A units, it depends on the connectivity pattern of the adenine bases (N7/N7 or N1/N1) and their rotamer states (head–head or head–tail), how large the acidifying effect is. Specifically, a series of trinuclear complexes with (A-N7)–Pt-(N7-A) and (A-N1)–Pt–(N1-A) cross-linking patterns and terminal 9-alkylguanine ligands (9MeGH, 9EtGH) have been analyzed in this respect, and it is shown that, for example, the 9MeA ligands in trans-,trans-,trans-[Pt(NH3)2(N7-9MeA-N1)2{Pt(NH3)2(9EtGH-N7)}2](ClO4)6·6H2O (4a) and trans-,trans-,trans-[Pt(NH3)2(N7-9EtA-N1)2{Pt(CH3NH2)2(9-MeGH-N7)}2](ClO4)6·3H2O (4b) are more acidic, by ca. 1.3units (first pKa), than the linkage isomer trans-,trans-,trans-[Pt(CH3NH2)2(N1-9MeA-N7)2{Pt(NH3)2(9MeGH-N7)}2](NO3)6·6.25H2O (1b). Overall, acidifications in these types of complexes amount to 7–9units, bringing the pKa values of such adenine ligands in the best case close to the physiological pH range. Comparison with pKa values of related trinuclear PtII complexes having different co-ligands at the Pt ions, confirms this picture and supports our earlier proposal that the close proximity of the exocyclic amino groups in a head–head arrangement of (A-N7)–Pt–(N7-A), and the stabilization of the resulting N6H–⋯H2N6 unit, is key to this difference.

Denaturation and electrophoresis of RNA with glyoxal.

This protocol is used to denature and separate large mRNA molecules (0.5-10 kb) on agarose gels by electrophoretic size fractionation. Glyoxal (also called diformyl or ethanedial), the agent responsible for maintaining denaturation in this protocol, contains two carbonyl groups that react to form a cyclic ring structure with the imino and amino groups of guanine. It can also react with the amino groups of adenine and cytidine. When RNA is denatured in the presence of glyoxal, this covalent adduct prevents normal base pairing and maintains the RNA in a denatured state in agarose gels. Once formed, these adducts are stable at room temperature at pH <7.0; thus, there is no need to add glyoxal to the gel or to the gel buffers to maintain the RNA in the denatured state. Because the fully denatured RNA migrates through agarose gels according to its molecular mass, this method can be used to accurately size mRNA molecules. Following electrophoresis and reversal of glyoxalation, the RNA can be detected using a northern hybridization procedure.