LATERAL VARIATION AND CONTROL OF THE REFRACTIVE INDEX AND THE TWO-DIMENSIONAL BOUND STATES IN GaAs/GaAIAs SUPERLATTICE STRUCTURES

In multiquantum-well and superlattice structures the physical properties - e.g. the energy of bound states and the refractive index - strongly depend on the superlattice periodicity. On the other side, the growth rate of the GaAs and GaAIAs is very sensitive to the crystallographical orientation. Applying these properties using nonplanar substrates multiquantum-well structures were grown, where the lattice periodicity were different in the different directions. The structures grown into GaAs grooves or onto linear mesa-structures have boundary planes along their axis where the refractive index perpendicular to the axis was lower than along the axis. This results in a strong wave-guiding making possible to develop a new type of semiconductor laserdiode

A genome-wide screen for essential yeast genes that affect telomere length maintenance

Telomeres are structures composed of repetitive DNA and proteins that protect the chromosomal ends in eukaryotic cells from fusion or degradation, thus contributing to genomic stability. Although telomere length varies between species, in all organisms studied telomere length appears to be controlled by a dynamic equilibrium between elongating mechanisms (mainly addition of repeats by the enzyme telomerase) and nucleases that shorten the telomeric sequences. Two previous studies have analyzed a collection of yeast deletion strains (deleted for nonessential genes) and found over 270 genes that affect telomere length (Telomere Length Maintenance or TLM genes). Here we complete the list of TLM by analyzing a collection of strains carrying hypomorphic alleles of most essential genes (DAmP collection). We identify 87 essential genes that affect telomere length in yeast. These genes interact with the nonessential TLM genes in a significant manner, and provide new insights on the mechanisms involved in telomere length maintenance. The newly identified genes span a variety of cellular processes, including protein degradation, pre-mRNA splicing and DNA replication

Novel Phosphorylation Sites in the S. cerevisiae Cdc13 Protein Reveal New Targets for Telomere Length Regulation

The S. cerevisiae Cdc13 is a multifunctional protein with key roles in regulation of telomerase, telomere end protection, and conventional telomere replication, all of which are cell cycle-regulated processes. Given that phosphorylation is a key mechanism for regulating protein function, we identified sites of phosphorylation using nano liquid chromatography-tandem mass spectrometry (nanoLC-MS/MS). We also determined phosphorylation abundance on both wild type (WT) and a telomerase deficient form of Cdc13, encoded by the cdc13-2 allele, in both G1 phase cells, when telomerase is not active, and G2/M phase cells, when it is. We identified 21 sites of in vivo phosphorylation, of which only five had been reported previously. In contrast, phosphorylation of two in vitro targets of the ATM-like Tel1 kinase, S249 and S255, was not detected. This result helps resolve conflicting data on the importance of phosphorylation of these residues in telomerase recruitment. multiple residues showed differences in their cell cycle pattern of modification. For example, phosphorylation of S314 was significantly higher in the G2/M compared to the G1 phase and in WT versus mutant Cdc13, and a S314D mutation negatively affected telomere length. Our findings provide new targets in a key telomerase regulatory protein for modulation of telomere dynamics. [Image: see text

Localization of telomeres and telomere-associated proteins in telomerase-negative Saccharomyces cerevisiae

Cells lacking telomerase cannot maintain their telomeres and undergo a telomere erosion phase leading to senescence and crisis in which most cells become nonviable. On rare occasions survivors emerge from these cultures that maintain their telomeres in alternative ways. The movement of five marked telomeres in Saccharomyces cerevisiae was followed in wild-type cells and through erosion, senescence/crisis and eventual survival in telomerase-negative (est2::HYG) yeast cells. It was found that during erosion, movements of telomeres in est2::HYG cells were indistinguishable from wild-type telomere movements. At senescence/crisis, however, most cells were in G2 arrest and the nucleus and telomeres traversed back and forth across the bud neck, presumably until cell death. Type I survivors, using subtelomeric Y′ amplification for telomere maintenance, continued to show this aberrant telomere movement. However, Type II survivors, maintaining telomeres by a sudden elongation of the telomere repeats, became indistinguishable from wild-type cells, consistent with growth properties of the two types of survivors. When telomere-associated proteins Sir2p, Sir3p and Rap1p were tagged, the same general trend was seen—Type I survivors retained the senescence/crisis state of protein localization, while Type II survivors were restored to wild type