The msh2 Gene of Schizosaccharomyces pombe Is Involved in Mismatch Repair, Mating-Type Switching, and Meiotic Chromosome Organization

We have identified in the fission yeast Schizosaccharomyces pombe a MutS homolog that shows highest homology to the Msh2 subgroup. msh2 disruption gives rise to increased mitotic mutation rates and increased levels of postmeiotic segregation of genetic markers. In bandshift assays performed with msh2Δ cell extracts, a general mismatch-binding activity is absent. By complementation assays, we showed that S. pombe msh2 is allelic with the previously identified swi8 and mut3 genes, which are involved in mating-type switching. The swi8-137 mutant has a mutation in the msh2 gene which causes a truncated Msh2 peptide lacking a putative DNA-binding domain. Cytological analysis revealed that during meiotic prophase of msh2-defective cells, chromosomal structures were frequently formed; such structures are rarely found in the wild type. Our data show that besides having a function in mismatch repair, S. pombe msh2 is required for correct termination of copy synthesis during mating-type switching as well as for proper organization of chromosomes during meiosis.     

The struggle of a good friend getting old: cellular senescence in viral responses and therapy

Cellular senescence is a state of stable cell cycle arrest associated with macromolecular alterations and secretion of pro‐inflammatory cytokines and molecules. Senescence‐associated phenotypes restrict damage propagation and activate immune responses, two essential processes involved in response to viral infections. However, excessive accumulation and persistence of senescent cells can become detrimental and promote pathology and dysfunctions. Various pharmacological interventions, including antiviral therapies, lead to aberrant and premature senescence. Here, we review the molecular mechanisms by which viral infections and antiviral therapy induce senescence. We highlight the importance of these processes in attenuating viral dissemination and damage propagation, but also how prematurely induced senescent cells can promote detrimental adverse effects in humans. We describe which sequelae due to viral infections and treatment can be partly due to excessive and aberrant senescence. Finally, we propose that pharmacological strategies which eliminate senescent cells or suppress their secretory phenotype could mitigate side effects and alleviate the onset of additional morbidities. These strategies can become extremely beneficial in patients recovering from viral infections or undergoing antiviral therapy.     

Assessing support for Blaberoidea phylogeny suggests optimal locus quality

Phylogenomics seeks to use next‐generation data to robustly infer an organism's evolutionary history. Yet, the practical caveats of phylogenomics motivate investigation of improved efficiency, particularly when quality of phylogenies are questionable. To achieve improvements, one goal is to maintain or enhance the quality of phylogenetic inference while severely reducing dataset size. We approach this by assessing which kinds of loci in phylogenomic alignments provide the majority of support for a phylogenetic inference of cockroaches in Blaberoidea. We examine locus substitution rate, saturation, evolutionary divergence, rate heterogeneity, stabilizing selection, and a priori information content as traits that may determine optimality. Our controlled experimental design is based on 265 loci for 102 blaberoidean taxa and 22 outgroup species. Loci with high substitution rate, low saturation, low sequence distance, low rate heterogeneity, and strong stabilizing selection derive more support for phylogenetic relationships. We found that some phylogenetic information content estimators may not be meaningful for assessing information content a priori. We use these findings to design concatenated datasets with an optimized subsample of 100 loci. The tree inferred from the optimized subsample alignment was largely identical to that inferred from all 265 loci but with less evidence of long branch attraction, improved statistical support, and potential 4‐6x improvements to computation time. Supported by phylogenetic and morphological evidence, we erect three newly named clades (Anallactinae Evangelista & Wipfler subfam. nov., Orkrasomeria tax. nov. Evangelista, Wipfler, & Béthoux and Hemithyrsocerini Evangelista tribe nov.) and propose other taxonomic modifications. The diagnosis of Pseudophyllodromiidae Grandcolas, 1996 is modified to accommodate Anallactinae and Pseudophyllodromiinae Vickery & Kevan, 1983. The diagnosis of Ectobiidae Brunner von Wattenwyl, 1865 is modified to add novel morphological characters.     

Effect of dieldrin toxicity on acetate and palmitate metabolism in rat liver.

The effect of a single oral dose of dieldrin (30 mg/kg body weight) on lipid metabolism in rats was studied. Liver lipids content increased and this increase was mainly in the triglyceride fraction. The incorporation of acetate-14C into fatty acids was decreased indicating an inhibition of lipogenesis. Fatty acid oxidation was increased. Palmitate-14C incorporation into the triglyceride fraction was enhanced pointing to an overall increased utilization of fatty acids.     

Presence of gamma glutamyl transferase in Mycobacterium smegmatis

The presence of gamma glutamyl transferase (GGT) has been established in Mycobacterium smegmatis. The 10,000 x g supernatant demonstrated only hydrolase activity and did not exhibit any transpeptidase activity. Most of the transferase activity was recovered in 100,000 x g supernatant demonstrating that GGT is a cytosolic enzyme. Maximum activity of GGT was observed at two days of growth and the activity decreased significantly till the seventh day of growth when mycobacteria was grown as stationary culture. The km for gamma glutamyl-p-nitroanilide was found to be 0.074 mM and Vmax for the reaction approached 11.9 nmol per min per mg protein. L-serine + borate was found to be a competitive inhibitor (Ki 12.05 mM) for GGT activity. The pH optimum for GGT activity was observed between 7.5 to 8.5 and temperature above 35 degrees C rapidly inactivated the enzyme activity. To the best of our knowledge, this is the first report which unequivocally establishes the presence of GGT activity in 10,000 x g supernatant of M. smegmatis.     

Nucleotide sequence of phenylalanine transfer RNA from Schizosaccharomyces pombe: implications for transfer RNA recognition by yeast phenylalanyl-tRNA synthetase.

The nucleotide sequence of Schizosaccharomyces pombe tRNAPhe was determined to be pG-U-C-G-C-A-A-U-G**-G*-U-G-psi-A-G-D-D-G-G-G-A-G-C-A-psi-G*-A-C-A-G-A-Cm-U-Gm-A-A-Y-A-psi-m5C-U-G-U-U-G-m7G-U*-C-A-U-C-G-G-T-psi-C-G-A-U-C-C-C-G-G-U-U-U-G-U-G-A-C-A-C-C-AOH. This sequence differs from that of S. cerevisiae tRNAPhe in 27 nucleotides. Saccharomyces cerevisiae phenylalanyl-tRNA synthetase aminoacylates both the homologous tRNAPhe and S. pombe t-NAPhe; the reactions have similar Km and Vmax values. However, the nucleotide sequence in the D stem is different in the two tRNAs. This region was proposed by Roe, B., et al. [(1973) Biochemistry 12, 4146--4154] to be the major recognition site for yeast phenylalanyl-tRNA synthetase, but the present results cast doubt on the validity of this hypothesis.     

Caffeine affects adventitious rooting and causes biochemical changes in the hypocotyl cuttings of mung bean (<Emphasis Type="Italic">Phaseolus aureus</Emphasis> Roxb.)

Caffeine (1,3,7-trimethylxanthine), a purine alkaloid found naturally in over 100 plant species, has recently been viewed as a safe chemical for management of pests including molluscs, slugs, snails, bacteria, and as a bird deterrent. It possesses phytotoxicity against plant species, yet the mechanism of action is lacking. A study was conducted to determine the effect of caffeine on the rooting of hypocotyl cuttings of mung bean (Phaseolus aureus) and the associated biochemical changes. At lower concentrations (<1,000 μM) of caffeine, though rooting potential was not affected, yet there was a significant decrease in the number of roots and root length. At 1,000 μM caffeine, there was a 68% decrease in the number of roots/primordia per cutting, whereas root length decreased by over 80%. However, no root formation occurred at 2,000 μM caffeine. Further investigations into the biochemical processes linked to root formation revealed that caffeine significantly affects protein content, activities of proteases, polyphenol oxidases (PPO) and total endogenous phenolic (EP) content, in the mung bean hypocotyls. A decrease in rooting potential was associated with a drastic reduction in protein content in the lower rooted portion, whereas the specific activity of proteases increased indicating that caffeine affects the protein metabolism. Activity of PPO decreased in response to caffeine, whereas EP content increased significantly indicating its non-utilization and thus less or no root formation. Respiratory ability of rooted tissue, as determined through TTC (2,3,5-triphenyl tetrazolium chloride) reduction, was impaired in response to caffeine indicating an adverse effect on the energy metabolism. The study concludes that caffeine interferes with the root development by impairing protein metabolism, affecting activity of PPO (and thus lignification), and EP content, which are the crucial steps for root formation.