eIF4F-like complexes formed by cap-binding homolog TbEIF4E5 with TbEIF4G1 or TbEIF4G2 are implicated in post-transcriptional regulation in Trypanosoma brucei

Members of the eIF4E mRNA cap-binding family are involved in translation and the modulation of transcript availability in other systems as part of a three-component complex including eIF4G and eIF4A. The kinetoplastids possess four described eIF4E and five eIF4G homologs. We have identified two new eIF4E family proteins in Trypanosoma brucei, and define distinct complexes associated with the fifth member, TbEIF4E5. The cytosolic TbEIF4E5 protein binds cap 0 in vitro. TbEIF4E5 was found in association with two of the five TbEIF4Gs. TbIF4EG1 bound TbEIF4E5, a 47.5-kDa protein with two RNA-binding domains, and either the regulatory protein 14-3-3 II or a 117.5-kDa protein with guanylyltransferase and methyltransferase domains in a potentially dynamic interaction. The TbEIF4G2/TbEIF4E5 complex was associated with a 17.9-kDa hypothetical protein and both 14-3-3 variants I and II. Knockdown of TbEIF4E5 resulted in the loss of productive cell movement, as evidenced by the inability of the cells to remain in suspension in liquid culture and the loss of social motility on semisolid plating medium, as well as a minor reduction of translation. Cells appeared lethargic, as opposed to compromised in flagellar function per se. The minimal use of transcriptional control in kinetoplastids requires these organisms to implement downstream mechanisms to regulate gene expression, and the TbEIF4E5/TbEIF4G1/117.5-kDa complex in particular may be a key player in that process. We suggest that a pathway involved in cell motility is affected, directly or indirectly, by one of the TbEIF4E5 complexes.

Melting-induced enhancement of the second-harmonic generation from metal nanoparticles

We report on the generation of second-harmonic signals by irradiating monolayers of high purity Ga nanoparticles, embedded in a SiOx matrix, with femtosecond laser pulses at 800 nm. A remarkable melting-induced enhancement of the second-harmonic generation is observed in correspondence of the phase transition. In addition, the hysteresis cycle of nonlinear transmittance is shown to be amplified a factor of 80-100 with respect to the linear response and interpreted in the framework of a nonlinear effective-medium model.

Grazing incidence toroidal mirror pairs in imaging and spectroscopic applications

The optical performance of pairs of toroidal mirrors in grazing incidence has been studied analytically and numerically. Two types of toroidal surface are possible: football and bicycle tire. In grazing incidence and for configurations that compensate up to second-order aberrations, there are significant differences in performance between the two types. For football-type tori the best configuration appears to be Z-shaped with tangential and sagittal foci at the middle point between the mirrors. For bicycle tire-type tori the best configuration is U-shaped with the tangential focus at the middle point and the sagittal at infinity.

Grazing-incidence high-resolution stigmatic spectrograph with two optical elements

Using two optical toroidal elements, a mirror and a grating, both working at grazing incidence, a spectrometer can be built that is stigmatic in the XUV region at one wavelength. Good compensation of the aberrations is achieved when the intermediate sagittal image is nearly at infinity. By varying the angle of incidence on the grating with simple movements, a given couple of optical elements could cover stigmatically a rather extended spectral range. If coupled with bidimensional array detectors, such a spectrograph could find applications in planned solar XUV telescopes.

Grazing incidence spectrograph-monochromator with a focusing toroidal mirror

The use of a toroidal mirror in front of a spherical grating spectrograph working at grazing incidence provides a system that is stigmatic in one dimension in the extreme ultraviolet (XUV) region and allows spectroscopy with space resolution. The system is optimized for spectral and spatial resolution and for efficiency. By using three toroidal mirrors mounted on a suitable turret and a new model of grazing incidence spectrometer, the system is capable of covering the whole XUV region. All the necessary movements are internal to the system and do not involve the source. Two examples are treated, one for a diagnostic study of laser-produced pellets and another for observation of large plasma machines.

Grazing incidence spectrograph-monochromator for xuv spectroscopy in the 5-900 A region

A combination grazing incidence spectrograph for photographic recording and scanning monochromator has been realized. The instrument is of a modular concept and all the internal components like the grating, the plateholder, and the scanning exit slit are easily removable. The radius of curvature of the Rowland cylinder can also be easily changed. The entrance beam is always kept fixed in position and direction, allowing the instrument to be permanently aligned with fixed light sources. The vacuum case is mechanically independent from the optical components.