Design and realisation of a MZI type polymer based high speed EO-modulator

We designed a 20 GHz Mach Zehnder interferometric EO-modulator based on a new developed polyesterimide. Measurements show a V/sub /spl pi// of 7.5 V, an insertion loss of 11 dB and an extinction ratio exceeding 20 dB for an interaction length of 2 cm

Structural determinants of TAR RNA-DNA annealing in the absence and presence of HIV-1 nucleocapsid protein

Annealing of the TAR RNA hairpin to the cTAR DNA hairpin is required for the minus-strand transfer step of HIV-1 reverse transcription. HIV-1 nucleocapsid protein (NC) plays a crucial role by facilitating annealing of the complementary hairpins. To gain insight into the mechanism of NC-mediated TAR RNA–DNA annealing, we used structural probes (nucleases and potassium permanganate), gel retardation assays, fluorescence anisotropy and cTAR mutants under conditions allowing strand transfer. In the absence of NC, cTAR DNA-TAR RNA annealing depends on nucleation through the apical loops. We show that the annealing intermediate of the kissing pathway is a loop–loop kissing complex involving six base-pairs and that the apical stems are not destabilized by this loop–loop interaction. Our data support a dynamic structure of the cTAR hairpin in the absence of NC, involving equilibrium between both the closed conformation and the partially open ‘Y’ conformation. This study is the first to show that the apical and internal loops of cTAR are weak and strong binding sites for NC, respectively. NC slightly destabilizes the lower stem that is adjacent to the internal loop and shifts the equilibrium toward the ‘Y’ conformation exhibiting at least 12 unpaired nucleotides in its lower part

Sensing peptide–oligonucleotide interactions by a two-color fluorescence label: application to the HIV-1 nucleocapsid protein

We present a new methodology for site-specific sensing of peptide–oligonucleotide (ODN) interactions using a solvatochromic fluorescent label based on 3-hydroxychromone (3HC). This label was covalently attached to the N-terminus of a peptide corresponding to the zinc finger domain of the HIV-1 nucleocapsid protein (NC). On interaction with target ODNs, the labeled peptide shows strong changes in the ratio of its two emission bands, indicating an enhanced screening of the 3HC fluorophore from the bulk water by the ODN bases. Remarkably, this two-color response depends on the ODN sequence and correlates with the 3D structure of the corresponding complexes, suggesting that the 3HC label monitors the peptide–ODN interactions site-specifically. By measuring the two-color ratio, we were also able to determine the peptide–ODN-binding parameters and distinguish multiple binding sites in ODNs, which is rather difficult using other fluorescence methods. Moreover, this method was found to be more sensitive than the commonly used steady-state fluorescence anisotropy, especially in the case of small ODNs. The described methodology could become a new universal tool for investigating peptide–ODN interactions

The conserved N-terminal basic residues and zinc-finger motifs of HIV-1 nucleocapsid restrict the viral cDNA synthesis during virus formation and maturation

Reverse transcription of the genomic RNA by reverse transcriptase occurs soon after HIV-1 infection of target cells. The viral nucleocapsid (NC) protein chaperones this process via its nucleic acid annealing activities and its interactions with the reverse transcriptase enzyme. To function, NC needs its two conserved zinc fingers and flanking basic residues. We recently reported a new role for NC, whereby it negatively controls reverse transcription in the course of virus formation. Indeed, deleting its zinc fingers causes reverse transcription activation in virus producer cells. To investigate this new NC function, we used viruses with subtle mutations in the conserved zinc fingers and its flanking domains. We monitored by quantitative PCR the HIV-1 DNA content in producer cells and in produced virions. Results showed that the two intact zinc-finger structures are required for the temporal control of reverse transcription by NC throughout the virus replication cycle. The N-terminal basic residues also contributed to this new role of NC, while Pro-31 residue between the zinc fingers and Lys-59 in the C-terminal region did not. These findings further highlight the importance of NC as a major target for anti-HIV-1 drugs

Identification of a methylated oligoribonucleotide as a potent inhibitor of HIV-1 reverse transcription complex

Upon HIV-1 infection of a target cell, the viral reverse transcriptase (RT) copies the genomic RNA to synthesize the viral DNA. The genomic RNA is within the incoming HIV-1 core where it is coated by molecules of nucleocapsid (NC) protein that chaperones the reverse transcription process. Indeed, the RT chaperoning properties of NC extend from the initiation of cDNA synthesis to completion of the viral DNA. New and effective drugs against HIV-1 continue to be required, which prompted us to search for compounds aimed at inhibiting NC protein. Here, we report that the NC chaperoning activity is extensively inhibited in vitro by small methylated oligoribonucleotides (mODN). These mODNs were delivered intracellularly using a cell-penetrating-peptide and found to impede HIV-1 replication in primary human cells at nanomolar concentrations. Extensive analysis showed that viral cDNA synthesis was severely impaired by mODNs. Partially resistant viruses with mutations in NC and RT emerged after months of passaging in cell culture. A HIV-1 molecular clone (NL4.3) bearing these mutations was found to replicate at high concentrations of mODN, albeit with a reduced fitness. Small, methylated ODNs such as mODN-11 appear to be a new type of highly potent inhibitor of HIV-1

The RNA annealing mechanism of the HIV-1 Tat peptide: conversion of the RNA into an annealing-competent conformation

The annealing of nucleic acids to (partly) complementary RNA or DNA strands is involved in important cellular processes. A variety of proteins have been shown to accelerate RNA/RNA annealing but their mode of action is still mainly uncertain. In order to study the mechanism of protein-facilitated acceleration of annealing we selected a short peptide, HIV-1 Tat(44–61), which accelerates the reaction efficiently. The activity of the peptide is strongly regulated by mono- and divalent cations which hints at the importance of electrostatic interactions between RNA and peptide. Mutagenesis of the peptide illustrated the dominant role of positively charged amino acids in RNA annealing—both the overall charge of the molecule and a precise distribution of basic amino acids within the peptide are important. Additionally, we found that Tat(44–61) drives the RNA annealing reaction via entropic rather than enthalpic terms. One-dimensional-NMR data suggest that the peptide changes the population distribution of possible RNA structures to favor an annealing-prone RNA conformation, thereby increasing the fraction of colliding RNA molecules that successfully anneal

Transient RNA–protein interactions in RNA folding

The RNA folding trajectory features numerous off-pathway folding traps, which represent conformations that are often equally as stable as the native functional ones. Therefore, the conversion between these off-pathway structures and the native correctly folded ones is the critical step in RNA folding. This process, referred to as RNA refolding, is slow, and is represented by a transition state that has a characteristic high free energy. Because this kinetically limiting process occurs in vivo, proteins (called RNA chaperones) have evolved that facilitate the (re)folding of RNA molecules. Here, we present an overview of how proteins interact with RNA molecules in order to achieve properly folded states. In this respect, the discrimination between static and transient interactions is crucial, as different proteins have evolved a multitude of mechanisms for RNA remodeling. For RNA chaperones that act in a sequence-unspecific manner and without the use of external sources of energy, such as ATP, transient RNA–protein interactions represent the basis of the mode of action. By presenting stretches of positively charged amino acids that are positioned in defined spatial configurations, RNA chaperones enable the RNA backbone, via transient electrostatic interactions, to sample a wider conformational space that opens the route for efficient refolding reactions

Etude spectroscopique et photophysique du transfert electronique intramoleculaire dans des composes de coordination. Implications pour l'electronique moleculaire

SIGLEINIST T 77104 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

PEOCOC project C1 doped G1 EO polymer preliminary characteristics

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : AR 16485 (1); AR 16485 (2) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueMinistere de la Recherche et de l'Espace (MRE), 75 - Paris (France)FRFranc