High-resolution Denaturing Gel Electrophoresis Research Articles

Measuring Poly-Adenosine Tail Length of RNAs by High-Resolution Northern Blotting Coupled with RNase H Cleavage.

The poly-adenosine, or poly(A) tail, plays key roles in controlling the stability and translation of messenger RNAs in all eukaryotes, and, as such, facile assays that can measure poly(A) length are needed. This chapter describes an approach that couples RNase H-mediated cleavage of an RNA of interest with high-resolution denaturing gel electrophoresis and northern blot-based detection. Major advantages of this method include the ability to directly measure the abundance of any RNA and the length of its poly(A) tail without amplification steps. The assay provides high specificity, sensitivity, and reproducibility for accurate quantitation using standard molecular biology equipment and reagents. Overall, the high-resolution northern blotting approach offers a cost-effective means of poly(A) RNA analysis that is especially useful for small numbers of transcripts and comparisons between experimental conditions or time points.

DNA Interstrand Crosslinks by H-pin Polyamide (S)-seco-CBI Conjugates.

Although DNA interstrand crosslinking (ICL) agents are widely used as antitumor drugs, DNA sequence-specific ICL agents are quite rare. In this study, H-pin imidazole-pyrrole polyamide 1-(chloromethyl)-2,3-dihydro-1H-benzo[e]indol-5-ol (seco-CBI) conjugates that produce sequence-specific DNA ICLs were designed and synthesized. Conjugates with H-pin polyamide and seco-CBI moieties were constructed to recognize a 7 bp DNA sequence, and their reactivity and selectivity in DNA alkylation were evaluated by using high-resolution denaturing gel electrophoresis and sequence-specific plasmid cleavage. One conjugate (6), which contained a chiral (S)-seco-CBI, exhibited greater sequence-specific ICL activity toward the target DNA sequence and was cytotoxic to a cancer cell line. Molecular modeling studies indicated that the greater activity of 6 resulted from the relative orientation of the cyclopropane group in the (S)-CBI unit.

Sequence-specific DNA alkylation by tandem Py-Im polyamide conjugates.

Tandem N-methylpyrrole-N-methylimidazole (Py-Im) polyamides with good sequence-specific DNA-alkylating activities have been designed and synthesized. Three alkylating tandem Py-Im polyamides with different linkers, which each contained the same moiety for the recognition of a 10 bp DNA sequence, were evaluated for their reactivity and selectivity by DNA alkylation, using high-resolution denaturing gel electrophoresis. All three conjugates displayed high reactivities for the target sequence. In particular, polyamide 1, which contained a β-alanine linker, displayed the most-selective sequence-specific alkylation towards the target 10 bp DNA sequence. The tandem Py-Im polyamide conjugates displayed greater sequence-specific DNA alkylation than conventional hairpin Py-Im polyamide conjugates (4 and 5). For further research, the design of tandem Py-Im polyamide conjugates could play an important role in targeting specific gene sequences.

Sequence‐Specific DNA Alkylation Targeting for Kras Codon 13 Mutation by Pyrrole–Imidazole Polyamide seco‐CBI Conjugates

Hairpin N-methylpyrrole-N-methylimidazole polyamide seco-CBI conjugates 2-6 were designed for synthesis by Fmoc solid-phase synthesis, and their DNA-alkylating activities against the Kras codon 13 mutation were compared by high-resolution denaturing gel electrophoresis with 225 base pair (bp) DNA fragments. Conjugate 5 had high reactivity towards the Kras codon 13 mutation site, with alkylation occurring at the A of the sequence 5'-ACGTCACCA-3' (site 2), including minor 1 bp-mismatch alkylation against wild type 5'-ACGCCACCA-3' (site 3). Conjugate 6, which differs from conjugate 5 by exchanging one Py unit with a β unit, showed high selectivity but only weakly alkylated the A of 5'-ACGTCACCA-3' (site 2). The hairpin polyamide seco-CBI conjugate 5 thus alkylates according to Dervan's pairing rule with the pairing recognition which β/β pair targets T-A and A-T pairs. SPR and a computer-minimized model suggest that 5 binds to the target sequence with high affinity in a hairpin conformation, allowing for efficient DNA alkylation.

Synthesis of Pyrrole–Imidazole Polyamide seco-1-Chloromethyl-5-hydroxy-1,2-dihydro-3H-benz[e]indole Conjugates with a Vinyl Linker Recognizing a 7 bp DNA Sequence

Convergent synthetic routes for N-methylpyrrole (P) and N-methylimidazole (I) seco-1-chloromethyl-5-hydroxy-1,2-dihydro-3H-benz[e]indole (CBI) conjugates with a vinyl linker were developed. New hairpin polyamide-seco-CBI conjugates, compounds 16-19, were synthesized, and their DNA sequence-specific alkylating activities were evaluated via high-resolution denaturing gel electrophoresis and high-performance liquid chromatography (HPLC) product analysis. The new synthetic route for PI conjugates with a vinyl linker consisted of the introduction of a vinylpyrrole unit (8-11) into the C terminal of a PI polyamide synthesized by (fluorenylmethoxy)carbonyl solid-phase peptide synthesis (SPPS), followed by liquid-phase coupling with seco-CBI. The yield of the conjugates was significantly improved compared with that of the method reported previously, which allows us to synthesize various substituted conjugates containing a vinyl linker. Conjugates 16-19 were designed to investigate the substituent effect of the vinyl linker, and conjugate 16S was synthesized to evaluate the reactivity between racemic and S enantiomers of the seco-CBI derivative. The results of high-resolution denaturing gel electrophoresis using 208 bp DNA fragments indicated that alkylation by compounds 16 and 17, in which the H of the vinyl linker of compound 16 was replaced with F, occurred predominantly at the A of the 5'-TTTGTCA-3' sequence at nanomolar concentrations. In clear contrast, compounds 18 and 19, which were methyl or Br derivatives of compound 16, did not exhibit any DNA alkylating activity. Moreover, HPLC product analysis using synthetic oligonucleotides demonstrated that alkylation occurred between the N3 of the adenine of the oligomer and the cyclopropane ring of 16S. Density functional calculation of substituted vinylpyrrole seco-CBI units indicated that methyl and Br substituents led to a significantly distorted geometry of the vinyl group with the pyrrole ring compared with H and F derivatives. Molecular modeling studies offered the additional information that steric hindrance reduced the DNA alkylating activity of these derivatives.

Requirement of β-alanine components in sequence-specific DNA alkylation by pyrrole–imidazole conjugates with seven-base pair recognition

To investigate the effect of incorporation of β-alanine in alkylating N-methylpyrrole (Py)– N-methylimidazole (Im) polyamide, seco-CBI conjugates 2– 8 were synthesized by an Fmoc solid-phase method and subsequent coupling with an alkylating moiety. DNA-alkylating activities of conjugates 2– 8 were evaluated by high-resolution denaturing gel electrophoresis with 202-base pair (bp) DNA fragments. Alkylation by conjugates 2 and 3, which have antiparallel pairings of β-alanine (β) opposite β (β/β) and Py/β, occurred mainly at the adenine (A) of the matching sequences, 5′-AGCTCC A-3′ (site 1) and 5′-AGCACC A-3′ (site 3). However, conjugate 4, with β/Py, did not show any DNA-alkylating activities. Similarly, conjugate 5, which possessed a Py/Py pair, weakly alkylated the matching sites at micromolar concentrations. Conjugates 6 and 7, which possessed β/β and Py/β pairs, respectively, alkylated at the A of the matching sequences, 5′-ACTACC A-3′ (site 2) and 5′-ACAACC A-3′ (site 4). In contrast, conjugated 8, with a Py/Py pair, showed lower activity and less alkylated DNA at sites 2 and 4 with mismatched alkylation at site 1 at a higher concentration than that of 6 and 7. These results demonstrate that incorporation of β-alanine is required for the sequence-specific alkylation by seco-CBI Py–Im conjugates with a seven-base pair sequence.

Efficient DNA Alkylation by a Pyrrole-Imidazole CBI Conjugate with an Indole Linker: Sequence-Specific Alkylation with Nine-Base-Pair Recognition

Conjugates 7, 8, and 10 of N-methylpyrrole (Py)-N-methylimidazole (Im) polyamides and 1,2,9,9a-tetrahydrocyclopropa[1,2-c]benz[1,2-e]indol-4-one (CBI) with a 5-amino-1H-indole-2-carbonyl linker were synthesized by Fmoc solid-phase synthesis and a subsequent liquid-phase coupling procedure. The DNA alkylating abilities of conjugates 7, 8, 6b, and 10 were examined using Texas Red-labeled PCR fragments and high-resolution denaturing gel electrophoresis. CBI conjugates 7 and 8 exhibited highly efficient sequence-specific DNA alkylation comparable with previous CBI conjugates with a vinyl linker. In particular, conjugate 10, with a 10-ringed hairpin Py-Im polyamide, alkylated at the adenine of 5'-ACAAATCCA-3'. Introduction of an indole linker greatly facilitated the synthesis of sequence-specific alkylating Py-Im polyamides.

Specific Adenine Alkylation by Pyrrole−Imidazole CBI Conjugates

We examined DNA alkylation by pyrrole (Py)-imidazole (Im) hairpin polyamides, which possess 1,2,9,9a-tetrahydrocyclopropa[1,2-c]benz[1,2-e]indol-4-one (CBI) or cyclopropapyrroloindole (CPI) as DNA alkylating moieties. High-resolution denaturing gel electrophoresis revealed that alkylation by CBI conjugates 2 and 4 occurred specifically at adenines (A) in matched sequences, whereas CPI conjugates 1 and 3 alkylated both A and guanines (G) in matched sequences. The origin of the different reactivity of CBI and CPI conjugates is discussed in relation to the electrophilicity of the cyclopropane moiety. The high selectivity of the CBI conjugate gives additional sequence specificity relative to CPI conjugates that would be useful for the biological applications.

Enantioselective DNA alkylation by a pyrrole-imidazole S-CBI conjugate.

Conjugates 12S and 12R of N-methylpyrrole (Py)-N-methylimidazole (Im) seven-ringed hairpin polyamide with both enantiomers of 1,2,9,9a-tetrahydrocyclopropa[1,2-c]benz[1,2-e]indol-4-one (CBI) were synthesized, and their DNA alkylating activity was examined. High-resolution denaturing gel electrophoresis revealed that 12S selectively and efficiently alkylated at one match sequence, 5'-TGACCA-3', in 450-bp DNA fragments. The selectivity and efficiency of the DNA alkylation by 12S were higher than those of the corresponding cyclopropapyrroloindole (CPI) conjugate, 11. In sharp contrast, another enantiomer, 12R, showed very weak DNA alkylating activity. Product analysis of the synthetic decanucleotide confirmed that the alkylating activity of 12S was comparable with 11 and that 12S had a significantly higher reactivity than 12R. The enantioselective reactivity of 12S and 12R is assumed to be due to the location of the alkylating cyclopropane ring of the CBI unit in the minor groove of the DNA duplex. Since the CBI unit can be synthesized from commercially available 1,3-naphthalenediol, the present results open up the possibility of large-scale synthesis of alkylating Py-Im polyamides for facilitating their use in future animal studies.

Molecular design of hairpin pyrrole-imidazole polyamides possessing sequence specific DNA alkylating moiety.

By conjugating pyrrole (Py)/imidazole (Im) hairpin polyamides with CBI, a stable alkylating moiety, we have developed a new type of DNA-sequence-specific alkylating agent. The sequence specificity and alkylation efficiency of the CBI conjugates were analyzed with high-resolution denaturing gel electrophoresis using linear 450- and 1000-bp DNA. The results demonstrate that CBI conjugates selectively alkylate adenine in specific sequences, whereas the previous type of alkylating polyamide, which contains segment A of DU-86, alkylates both adenine and guanine.

Molecular design of hairpin polyamide possessing sequence-specific alkylation activity.

A novel type of sequence specific hairpin polyamide alkylating agents were synthesized and their alkylation activities were evaluated on linear 450 bp DNA fragment. To optimize the design of hairpin polyamide CPI-conjugates, several structural analogues were prepared. Analysis using high resolution denaturing gel electrophoresis suggests that such subtle structural differences effect the sequence specificity of the polyamides.

Molecular design of a pyrrole-imidazole hairpin polyamides for effective DNA alkylation.

New hairpin polyamide-CPI (CPI = cyclopropylpyrroloindole) conjugates, compounds 12-14, were synthesized and their DNA-alkylating activities compared with the previously prepared hairpin polyamide, compound 1, by high-resolution denaturing gel electrophoresis with 450 base pair (bp) DNA fragments and by HPLC product analysis of the synthetic decanucleotide. In accord with our previous results, alkylation by compound 1 occurred predominantly at the G moiety of the sequence 5'-AGTCAG-3' (site 3). However, compound 12, in which the structure of the alkylating moiety of compound 1 is replaced with segment A of duocarmycin A DU-86 (CPI), did not show any DNA alkylating activity. In clear contrast, the hairpin CPI conjugate 13, which differs from compound 1 in that it lacks one Py unit and possesses a vinyl linker, alkylated the A of 5'-AGTCAG-3' (site 3) efficiently at nanomolar concentrations. Alkylation by compound 14, which has a vinyl linker, occurred at the A of 5'-AGTCCA-3' (site 6) and at several minor alkylation sites, including mismatch alkylation at A of 5'-TCACAA-3' (site 2). The significantly different reactivity of the alkylating hairpin polyamides 1, 12, 13, and 14 was further confirmed by HPLC product analysis by using a synthetic decanucleotide. The results suggest that hairpin polyamide--CPI conjugate 13 alkylates effectively according to Dervan's pairing rule, and with a new mode of recognition in which the Im-vinyl linker (L) pair targets G-C base pairs. These results demonstrate that incorporation of the vinyl-linker pairing with Im dramatically improves the reactivity of hairpin polyamide--CPI conjugates.

Molecular design of hairpin imidazole-pyrrole polyamide for effective DNA alkylation.

A new type of hairpin polyamide-CPI conjugate possessing a vinyl linker has been synthesized. Sequence-selective alkylation of double-stranded DNA by conjugates was investigated by high resolution denaturing gel electrophoresis using 450 bp DNA fragments. Highly-efficient DNA alkylation predominantly occurs at the purines of 5'-(A/T)G(T/A)CPu-3' site at nanomolar concentration.

Highly Cooperative DNA Dialkylation by the Homodimer of Imidazole−Pyrrole Diamide−CPI Conjugate with Vinyl Linker

We synthesized new type of diamide−CPI conjugate possessing a vinyl linker, 7. Sequence-selective alkylation of double-stranded DNA by 7 was investigated by high-resolution denaturing gel electrophoresis using ∼400 bp DNA fragments. Highly efficient alkylation predominantly occurs simultaneously at the purines of 5‘-PyG(A/T)CPu-3‘ site on both strands at a nanomolar concentration of 7. These results suggest that the homodimer of conjugate 7 dialkylates both strands according to Dervan's pairing rule together with a new mode of recognition in which the Im-vinyl linker (L) pair targets G/C base pairs. In addition to the major dialkylation sites, a minor alkylation site was also observed at 5‘-GT(A/T)GC-3‘. This alkylation can be explained by an analogous slipped homodimer recognition mode in which the L−L pair recognizes the A/T base pair. Efficient dialkylation by the homodimer of 7 was further confirmed using oligonucleotides (ODNs). HPLC analysis revealed that the conjugate 7 simultaneously alkylates GN3/AN3 of the target sequences on both strands of ODNs.

Rational Design of Sequence-Specific DNA Alkylating Agents Based on Duocarmycin A and Pyrrole−Imidazole Hairpin Polyamides

Synthesis of novel conjugates between segment A of Duocarmycin A (Du) and N-methylimidazole (Im)−N-methylpyrrole (Py) hairpin polyamides and their DNA alkylation are described. The conjugates PyPyPyγImPyPyDu (8a) and ImPyPyγImPyPyDu (8b) were designed to alkylate the target sequences (A/T)G(A/T)2N(A/G) and (A/T)G(A/T)CN(A/G), respectively, according to Dervan's ring-pairing rule. High-resolution denaturing gel electrophoresis indicated that 8a exclusively alkylated the A of the 5‘-TGTAAAA-3‘ within a ∼400 bp DNA fragment. Similarly, alkylation by 8b occurred exclusively at the G of the 5‘-AGTCAGA-3‘ sequence with efficiency at nanomolar concentration. To better understand the structure of the alkylated DNA by these conjugates, the alkylation of non-self-complementary duplex decanucleotides, ODN1 and ODN2, was investigated. HPLC and ESMS analyses of the reaction of these ODNs with 8a and 8b demonstrated that both conjugates efficiently and selectively alkylate N3 of the purine bases of their target sequences.

Design, synthesis, and sequence selective DNA cleavage of functional models of bleomycin. 1. Hybrids incorporating a simple offal-complexing moiety of bleomycin and lexitropsin carriers.

The syntheses of functional models for bleomycin, which are composed of a simple analog of the metal-complexing moiety of bleomycin and oligo-N-methylpyrrole peptide DNA-binding moieties, are described. The extent and the relative rate of their cleavage of DNA in the presence of reductants were determined independently by an ethidium binding assay and by agarose gel electrophoresis experiments. The rate of DNA cleavage increases with the number of N-methylpyrrole units in the carrier moiety. The sequence selectivity of DNA cleavage was demonstrated by polyacrylamide sequencing gel electrophoresis of cleavage reactions on two 5'-32P labeled restriction fragments: a 158 bp GC-rich fragment from pBR322 and a 241 bp AT-rich fragment fragment from SV40. Comparison of the sequence selectivity with that of bleomycin A2 indicates that the poly-N-methylpyrrole moiety directs the hybrid compounds to AT-rich sequences of DNA. High-resolution denaturing gel electrophoresis of DNA cleaved by the model compounds reveals that 3' phosphate is produced exclusively, indicating that the chemistry of DNA cleavage differs from that of bleomycin.

Analysis of mosquito bloodmeals by DNA profiling

Human specific genetic markers have been used to profile the human DNA found within a mosquito bloodmeal. In this technique, variable numbers of tandem repeat (VNTR) sequences are employed to prime amplification of human DNA in the polymerase chain reaction (PCR) and the radiolabelled products are analysed by high resolution denaturing gel electrophoresis. Matching of DNA profiles allows identification of the individual human host. Bloodmeals of 125 female Anopheles gambiae Giles mosquitoes, caught dead or alive in verandah-trap huts wherein two people had slept overnight protected by intact insecticide-impregnated bednets, were analysed: thirty-five out of thirty-nine profiles generated were identical to those of the sleepers under the nets. Thus the blood-fed mosquitoes found after impregnated nets have been used cannot, in most cases, be explained away by entry of already fed mosquitoes into the huts.

Sequence-specific double-strand cleavage of DNA by penta-N-methylpyrrolecarboxamide-EDTA X Fe(II).

In the presence of O2 and 5 mM dithiothreitol, penta-N-methylpyrrolecarboxamide-EDTA X Fe(II) [P5E X Fe(II)] at 0.5 microM cleaves pBR322 plasmid DNA (50 microM in base pairs) on opposite strands to afford discrete DNA fragments as analyzed by agarose gel electrophoresis. High-resolution denaturing gel electrophoresis of a 32P-end-labeled 517-base-pair restriction fragment containing a major cleavage site reveals that P5E X Fe(II) cleaves 3-5 base pairs contiguous to a 6-base-pair sequence, 5'-T-T-T-T-T-A-3' (4,323-4,328 base pairs). The major binding orientation of the pentapeptide occurs with the amino terminus at the adenine side of this sequence. In the presence of 5 mM dithiothreitol, 0.01 microM P5E X Fe(II) converts form I pBR322 DNA at 0.22 microM plasmid (1.0 mM in base pairs) to 40% form II, indicating the cleavage reaction is catalytic, turning over a minimum of nine times. This synthetic molecule achieves double-strand cleavage of DNA (pH 7.9, 25 degrees C) at the 6-base-pair recognition level and may provide an approach to the design of "artificial restriction enzymes".