Emission and its back-reaction accompanying electron motion in relativistically strong and QED-strong pulsed laser fields.

The emission from an electron in the field of a relativistically strong laser pulse is analyzed. At pulse intensities of J>or=2x10(22) W/cm(2) the emission from counterpropagating electrons is modified by the effects of quantum electrodynamics (QED), as long as the electron energy is sufficiently high: E>or=1 GeV . The radiation force experienced by an electron is for the first time derived from the QED principles and its applicability range is extended toward the QED-strong fields.

Pair creation in QED-strong pulsed laser fields interacting with electron beams.

QED effects are known to occur in a strong laser pulse interaction with a counterpropagating electron beam, among these effects being electron-positron pair creation. We discuss the range of laser pulse intensities of J≥5×10(22) W/cm2 combined with electron beam energies of tens of GeV. In this regime multiple pairs may be generated from a single beam electron, some of the newborn particles being capable of further pair production. Radiation backreaction prevents avalanche development and limits pair creation. The system of integro-differential kinetic equations for electrons, positrons and γ photons is derived and solved numerically.

Drosophila poly(ADP-ribose) glycohydrolase mediates chromatin structure and SIR2-dependent silencing.

Protein ADP ribosylation catalyzed by cellular poly(ADP-ribose) polymerases (PARPs) and tankyrases modulates chromatin structure, telomere elongation, DNA repair, and the transcription of genes involved in stress resistance, hormone responses, and immunity. Using Drosophila genetic tools, we characterize the expression and function of poly(ADP-ribose) glycohydrolase (PARG), the primary enzyme responsible for degrading protein-bound ADP-ribose moieties. Strongly increasing or decreasing PARG levels mimics the effects of Parp mutation, supporting PARG's postulated roles in vivo both in removing ADP-ribose adducts and in facilitating multiple activity cycles by individual PARP molecules. PARP is largely absent from euchromatin in PARG mutants, but accumulates in large nuclear bodies that may be involved in protein recycling. Reducing the level of either PARG or the silencing protein SIR2 weakens copia transcriptional repression. In the absence of PARG, SIR2 is mislocalized and hypermodified. We propose that PARP and PARG promote chromatin silencing at least in part by regulating the localization and function of SIR2 and possibly other nuclear proteins.

Isolated attosecond pulses generated by relativistic effects in a wavelength-cubed focal volume.

Lasers that provide an energy encompassed in a focal volume of a few cubic wavelengths (lambda3) can create relativistic intensity with maximal gradients using minimal energy. With particle-in-cell simulations we found that single 200-as pulses could be produced efficiently in a lambda3 laser pulse reflection by means of deflection and phase compression caused by the coherent motion of the plasma electrons that emit these pulses. This novel technique is efficient (approximately 10%) and can produce single attosecond pulses from the millijoule to the joule level.

Stellate repeats: targets of silencing and modules causing cis-inactivation and trans-activation.

The mechanism of silencing of testis expressed X-linked Stellate repeats by homologous Y-linked Suppressor of Stellate [Su(Ste)] repeats localized in the crystal locus was studied. The double stranded RNA as a product of symmetrical transcription of Su(Ste) repeat and small interference Su(Ste) siRNA were revealed suggesting the mechanism of RNA interference (RNAi) for Stellate silencing. The relief of Stellate silencing as a result of impaired complementarity between the sequences of putative target Stellate transcripts and Su(Ste) repeats was shown. The role of RNAi mechanism in the silencing of heterochromatic retrotransposon GATE inserted in Stellate cluster was revealed. The studies of cis-effects of Stellate tandem repeats causing variegated expression of juxtaposed reporter genes were extended and the lacZ variegation in imaginal disc was shown. The exceptional case of a non-variegated expression of mini-white gene juxtaposed to Stellate repeats in a construct inserted into the 39C region was shown to be accompanied by trans-activation in homozygous state. Trans-activation effect was retained after transposition of this construct into heterochromatic environment in spite of strong variegation of a mini-white gene.