Comparative Analysis of DNA‐Binding Selectivity of Hairpin and Cyclic Pyrrole‐Imidazole Polyamides Based on Next‐Generation Sequencing

Many long pyrrole‐imidazole polyamides (PIPs) have been synthesized in the search for higher specificity, with the aim of realizing the great potential of such compounds in biological and clinical areas. Among several types of PIPs, we designed and synthesized hairpin and cyclic PIPs targeting identical sequences. Bind‐n‐Seq analysis revealed that both bound to the intended sequences. However, adenines in the data analyzed by the previously reported Bind‐n‐Seq method appeared to be significantly higher in the motif ratio than thymines, even though the PIPs were not expected to distinguish A from T. We therefore examined the experimental protocol and analysis pipeline in detail and developed a new method based on Bind‐n‐Seq motif identification with a reference sequence (Bind‐n‐Seq‐MR). High‐throughput sequence analysis of the PIP‐enriched DNA data by Bind‐n‐Seq‐MR presented A and T comparably. Surface plasmon resonance assays were performed to validate the new method.     

GaAs power m.e.s.f.e.t.s. with a graded recess structure

A new recess structure device was developed to improve the field distrubution and therfore the performance of GaAs power m.e.s.f.e.t.s. The linear gain and the output power were improved by 1?2 dB for this structure. The highest output powers obtained are 15 W with 4 dB associated gain at 6 GHz, and 4.3 W with 3 dB associated gain at 11 GHz.     

Ligand‐Mediated G‐Quadruplex Induction in a Double‐Stranded DNA Context by Cyclic Imidazole/Lysine Polyamide

G‐quadruplex (G4) DNA is often observed as a DNA secondary structure in guanine‐rich sequences, and is thought to be relevant to pharmacological and biological events. Therefore, G4 ligands have attracted great attention as potential anticancer therapies or in molecular probe applications. Here, we designed cyclic imidazole/lysine polyamide (cIKP) as a new class of G4 ligand. It was readily synthesized without time‐consuming column chromatography. cIKP selectively recognized particular G4 structures with low nanomolar affinity. Moreover, cIKP exhibited the ability to induce G4 formation of the promoter of G4‐containing DNA in the context of stable double‐stranded DNA (dsDNA) under molecular crowding conditions. This cIKP might be applicable as a molecular probe for the detection of potential G4‐forming sequences in dsDNA.     

Effect of ATRX and G‐Quadruplex Formation by the VNTR Sequence on α‐Globin Gene Expression

ATR‐X (α‐thalassemia/mental retardation X‐linked) syndrome is caused by mutations in chromatin remodeler ATRX. ATRX can bind the variable number of tandem repeats (VNTR) sequence in the promoter region of the α‐globin gene cluster. The VNTR sequence, which contains the potential G‐quadruplex‐forming sequence CGC(GGGGCGGGG)_n, is involved in the downregulation of α‐globin expression. We investigated G‐quadruplex and i‐motif formation in single‐stranded DNA and long double‐stranded DNA. The promoter region without the VNTR sequence showed approximately twofold higher luciferase activity than the promoter region harboring the VNTR sequence. G‐quadruplex stabilizers hemin and TMPyP4 reduced the luciferase activity, whereas expression of ATRX led to a recovery in reporter activity. Our results demonstrate that stable G‐quadruplex formation by the VNTR sequence downregulates the expression of α‐globin genes and that ATRX might bind to and resolve the G‐quadruplex.     

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.