The effect of cycloheximide upon polyribosome stability in two yeast mutants defective respectively in the initiation of polypeptide chains and in messenger RNA synthesis

Summary The effect of cycloheximide upon protein synthesis, RNA metabolism, and polyribosome stability was investigated in the parent and in two temperature-sensitive mutant yeast strains defective respectively in the initiation of polypeptide chains and in messenger RNA synthesis. Cycloheximide at high concentrations (100 g/ml) severely inhibits but does not completely stop protein synthesis (Fig. 1); the incorporation of ¹⁴C-amino acids into polyribosome-associated nascent polypeptide chains continues at a slow but measurable rate (Figs. 2 and 3). Polyribosome structures are stable in the parent strain at 36° whether or not cycloheximide is present (Fig. 5). However, in Mutant ts^- 136, a mutant defective in messenger as well as in stable RNA production, polyribosomes decay at the restrictive temperature (36° C) at the same rate whether or not cycloheximide is present (Fig. 5). Thus the maintenance of polyribosome structures is dependent upon the continued synthesis of messenger RNA even under conditions of extremely slow polypeptide chain elongation. In mutant ts^- 187, a mutant defective in the initiation of polypeptide chains, all of the polyribosomes decay to monoribosomes within 2 minutes after a shift to the restrictive temperature; cycloheximide completely prevents this decay demonstrating that this mutant is capable of continued messenger RNA synthesis at 36° C. Consistent with these observations is the fact that a newly synthesized heterogeneously sedimenting RNA fraction continues to enter polyribosomes in the presence of cycloheximide whereas the entrance of newly synthesized ribosomal RNA is severely inhibited (Figs. 7, 8, 9). The decay or lack of decay of polyribosomes at the restrictive temperature is, therefore, a rapid and discriminating test for the analysis of mutants defective in macromolecule synthesis. Mutants which exhibit a decay of polyribosomes in the presence of cycloheximide are likely to be defective directly or indirectly in the synthesis of messenger RNA whereas mutants in which decay is prevented or slowed by cycloheximide are likely to be defective in some factor required for the association of ribosomes and messenger RNA.     

A transcriptional network associated with natural variation in Drosophila aggressive behavior

Background  

Aggressive behavior is an important component of fitness in most animals. Aggressive behavior is genetically complex, with natural variation attributable to multiple segregating loci with allelic effects that are sensitive to the physical and social environment. However, we know little about the genes and genetic networks affecting natural variation in aggressive behavior. Populations of Drosophila melanogaster harbor quantitative genetic variation in aggressive behavior, providing an excellent model system for dissecting the genetic basis of naturally occurring variation in aggression.     

Aging in the post-genomic era: simple or complex?

A report on the Third Genetic Effects on Aging Meeting, The Jackson Laboratory, Bar Harbor, Maine, August 4-8, 2000.     

Mating of natural <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> strains for improved glucose fermentation and lignocellulosic inhibitor tolerance

Natural Saccharomyces cerevisiae isolates from vineyards in the Western Cape, South Africa were evaluated for ethanol production in industrial conditions associated with the production of second-generation biofuels. The strains displayed high phenotypic diversity including the ability to grow at 45 °C and in the presence of 20% (v/v) ethanol, strain YI13. Strains HR4 and YI30 were inhibitor-tolerant under aerobic and oxygen-limited conditions, respectively. Spore-to-spore hybridization generated progeny that displayed heterosis, including increased ethanol productivity and improved growth in the presence of a synthetic inhibitor cocktail. Hybrid strains HR4/YI30#6 and V3/YI30#6 were able to grow at a high salt concentration (2 mol/L NaCl) with V3/YI30#6 also able to grow at a high temperature (45 °C). Strains HR4/YI30#1 and #3 were inhibitor-tolerant, with strain HR4/YI30#3 having similar productivity (0.36 ± 0.0036 g/L per h) as the superior parental strain, YI30 (0.35 ± 0.0058 g/L per h). This study indicates that natural S. cerevisiae strains display phenotypic variation and heterosis can be achieved through spore-to-spore hybridization. Several of the phenotypes (temperature-, osmo-, and inhibitor tolerance) displayed by both the natural strains and the generated progeny were at the maximum conditions reported for S. cerevisiae strains.     

Evaluation of artificial selection in Standard Poodles using whole-genome sequencing

Identifying regions of artificial selection within dog breeds may provide insights into genetic variation that underlies breed-specific traits or diseases—particularly if these traits or disease predispositions are fixed within a breed. In this study, we searched for runs of homozygosity (ROH) and calculated the d _i statistic (which is based upon F _ST) to identify regions of artificial selection in Standard Poodles using high-coverage, whole-genome sequencing data of 15 Standard Poodles and 49 dogs across seven other breeds. We identified consensus ROH regions ≥1 Mb in length and common to at least ten Standard Poodles covering 0.6 % of the genome, and d _i regions that most distinguish Standard Poodles from other breeds covering 3.7 % of the genome. Within these regions, we identified enriched gene pathways related to olfaction, digestion, and taste, as well as pathways related to adrenal hormone biosynthesis, T cell function, and protein ubiquitination that could contribute to the pathogenesis of some Poodle-prevalent autoimmune diseases. We also validated variants related to hair coat and skull morphology that have previously been identified as being under selective pressure in Poodles, and flagged additional polymorphisms in genes such as ITGA2B, CBX4, and TNXB that may represent strong candidates for other common Poodle disorders.     

Variability in expression of common fragile sites: in search of a new criterion

Summary Fragile sites are nonrandom, heritable sites on chromosomes that can be induced to form gaps, breaks, and rearrangements under specific conditions. There is currently no established criterion to define a common fragile site. We applied seven published criteria to our data from three groups of subjects: (1) three pairs of like-sexed twins, (2) four unaffected von HippelLindau (VHL) family members, and (3) six patients affected with VHL disease. Substantial differences were present in the numbers of sites considered positive by these criteria. While some of this variability can be attributed to technical factors, our data illustrate the problems in comparing results from different studies to assess the significance of fragile sites. A recently published criterion is based upon the Poisson distribution. We found this criterion to be flawed in its presentation, and furthermore, the Poisson distribution did not provide an adequate approximation to our data. We propose here an alternative approach based upon the negative binomial distribution.