Influence of different inhibitors on the activity of theRAD54 dependent step of DNA repair inSaccharomyces cerevisiae

Summary The recombinagenic pathway of DNA repair in yeast was characterized by the effect of different inhibitors on the temperature-dependent survival after-irradiation in haploid cells of the thermoconditional mutantrad54-3. Blocking protein synthesis with cycloheximide in replicating cells caused partial inhibiton of theRAD54 dependent function but some repair activity remained detectable. This indicates that-rays can induceRAD54 activity above some constitutive level of function. Inhibition of DNA replication by hydroxyurea efficiently blocked theRAD54 dependent function in stationary-phase cells but not in logarithmic-phase cells. In logarithmic-phase cells, we found a strong inhibitory effect of caffeine on theRAD54 mediated repair process.     

Land use,rangeland degradation and ecological changes in the southern Kalahari,Botswana

Dual‐scale analyses assessing farm‐scale patterns of ecological change and landscape‐scale patterns of change in vegetation cover and animal distribution are presented from ecological transect studies away from waterpoints, regional remotely sensed analysis of vegetation cover and animal numbers across the southern Kalahari, Botswana. Bush encroachment is prevalent in semi‐arid sites where Acacia mellifera Benth. is widespread in communal areas and private ranches, showing that land tenure changes over the last 40 years have not avoided rangeland degradation. Herbaceous cover is dominated in intensively grazed areas by the annual grass Schmidtia kalahariensis Stent and in moderately grazed areas by the perennial grass Eragrostis lehmanniana Nees. Nutritious perennial grass species including Eragrostis pallens Hack. Ex Schinz remain prevalent in Wildlife Management Areas. Other ecological changes include the invasion of the exotic Prosopis glandulosa Torr. and dense stands of Rhigozum trichotomum Kuntze. in the arid southwest. Regional patterns of wildlife species show that the expansion of cattleposts and fenced ranches has led to large areas of low wildlife conservation value even in areas where cattle production is not practiced. Findings show the need for integrated landscape‐scale planning of land use if the ecological value and biodiversity of the southern Kalahari is to be retained.     

Anemia induces 5'-nucleotidase in fibroblasts of cortical labyrinth of rat kidney

We recently observed a strong increase of 5'-nucleotidase in renal fibroblasts of rats that were anemic due to an immunity against erythropoietin. In order to test if the change of 5'-nucleotidase was related with anemia, we studied the distribution of the enzyme in irradiated rats treated with phenylhydrazine. The hematocrit of these rats decreased to 15% within 4 days and erythropoietin levels were more than 200 times over controls. After 7 days a histochemical study showed that the enzymatic activity and the immunoreactivity for 5'-nucleotidase was markedly enhanced in the fibroblasts of the cortical labyrinth. There was no modification of 5'-nucleotidase in other cell types of the kidney. The 5'-nucleotidase activity of renal fibroblasts in cell culture increased by 72% upon addition of 160 microM 5'-AMP to the culture medium for 8 days. We propose that anemia provokes an energy deficit in some structure in the cortical labyrinth. This might increase the concentration of 5'-AMP which would induce 5'-nucleotidase. An interesting consequence of these events would be an increased production of adenosine in the direct vicinity of some of its putative targets, the glomerular arterioles and the erythropoietin-producing cells.     

Analysis of mutagenic DNA repair in a thermoconditional mutant of Saccharomyces cerevisiae. III. Dose-response pattern of mutation induction in UV-irradiated rev2ts cells

Summary Recent studies regarding the influence of cycloheximide on the temperature-dependent increase in survival and mutation frequencies of a thermoconditional rev2 mutant lead to the suggestion that the REV2-coded mutagenic repair function is UV-inducible. In the present study we show that stationary-phase rev2 ^ts cells are characterized by a biphasic linear-quadratic dose-dependence of mutation induction (mutation kinetics) of ochre alleles at 23° C (permissive temperature) but linear kinetics at the restrictive temperature of 36° C. Mathematical analysis using a model based on Poisson statistics and a further mathematical procedure, the calculation of apparent survival, support the assumption that the quadratic component of the reverse mutation kinetics investigated can be attributed to a UV-inducible component of mutagenic DNA repair controlled by the REV2 gene.     

Calmodulin antagonists increase the amount of mRNA for the low-density-lipoprotein receptor in skin fibroblasts.

The effects of calmodulin antagonists on the amount of LDL receptor (LDL-R) mRNA in cultured human fibroblasts was examined by hybridization with a fragment of LDL-R cDNA. In a 'Northern' blot the fragment hybridized to a 5.3-kilobase RNA, as expected for LDL-R mRNA. The concentration of this RNA was increased in preparations from cells that were treated with trifluoperazine or W-7 [N-(6-aminohexyl)-5-chloronaphthalene-1-sulphonamide]. The selectivity of the increase was established by using a probe for beta-actin mRNA. In dot-blot hybridization it was observed that the calmodulin antagonists cause 2-4-fold relative increase in the amount of LDL-R mRNA.     

Inducibility of error-prone DNA repair in yeast?

Whereas some experimental evidence suggests that mutagenesis in yeast after treatment with DNA-damaging agents involves inducible functions, a general-acting error-prone repair activity analogous to the SOS system of Escherichia coli has not yet been demonstrated. The current literature on the problem of inducibility of mutagenic repair in yeast is reviewed with emphasis on the differences in the experimental procedures applied.