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101.
Christopher W. Lawrence Beth R. Krauss Roshan B. Christensen 《Mutation research》1985,150(1-2):211-216
Previously isolated mutations in baker's yeast, Saccharomyces cerevisiae, that impair induced mutagenesis were all identified with the aid of tests that either exclusively or predominantly detect base-pair substitutions. To avoid this bias, we have screened 11 366 potentially mutant clones for UV-induced reversion of the frameshift allele, his4–38, and have identified 10 mutants that give much reduced yields of revertants. Complementation and recombination tests show that 6 of these carry mutations at the previously known REV1, REV1 and REV3 loci, while the remaining 4 define 3 new genes, REV4 (2 mutations), REV5 and REV6. The rev4 mutations are readily suppressed in many genetic backgrounds and, like the rev5 mutation, impart only a limited deficiency for induced mutagenesis: it is likely, therefore that the REV4+ and REV5+ gene functions are only remotely concerned with this process. The rev6 mutants have a more general deficiency, however, as well as marked sensitivity to UV and an increased spontaneous mutation rate, properties that suggest the REV6 gene is directly involved in mutation induction. The REV5 gene is located about 1 cM proximal to CYC1 on chromosome X. 相似文献
102.
The effect of phytoplankton and suspended sediment on the growth of Corbicula fluminea (Bivalvia) 总被引:3,自引:2,他引:1
Juvenile Corbicula fluminea Müller (1774) were cultured at 15.3 °C in the laboratory on eight combinations of suspended sediment and phytoplankton. Sediment concentrations were 2.6, 25, 50, and 150 mg l–1. Chlorophyll a levels were 15.6 and 62.5 µg l–1. Clam tissue growth was found to be independent of silt concentration but increased at the higher chlorophyll level (p < 0.05). The growth experiment was repeated at 24 °C with chlorophyll a concentrations of 18.9 and 112.6 µg l–1. Growth was again greater at the higher phytoplankton level (p < 0.05). These results demonstrate that Asiatic clam populations are food-limited most of the growing season in the Northern and Western portions of California's eutrophic Sacramento-San Joaquin Delta where chlorophyll a levels average less than the lower of these values. Comparisons of clam growth in the laboratory and estuary support the food limitation hypothesis as at the higher food concentration laboratory tissue growth was 2.3 and 3.8 times greater during the high and low temperature evaluations than in the estuary. 相似文献
103.
We have isolated Neurospora trehalaseless mutants and mapped the trehalase structural gene to linkage group I. The structural gene mutations not only affect thermostability and other characteristics of the enzyme but also affect the production of an inhibitor of the wild-type trehalase. The inhibitor appears to be the mutant trehalase. We suggest that the mutant subunits act as inhibitors by entering into the multimeric forms of the enzyme and altering the ability of the normal wild-type subunits to catalyze the cleavage of trehalose.—Wild type trehalase has been purified to near homogeneity, and its characteristics have been studied. It was purified as a tetramer, with each subunit having a molecular weight of 88,000.—We have studied the regulation of trehalase and found the production of trehalase to be glucose repressible. Cells begin to produce trehalase 60 min after being transferred to glucose-free medium. 相似文献
104.
Concentrations of Cu, Ag and Zn were measured in the soft tissues of the estuarine bivalve Macoma balthica in South San Francisco Bay at near-monthly intervals for periods of two to three years at four stations, and eight years at a metal-enriched station. The amplitude and frequency of fluctuations differed among stations and among metals. Fluctuations were greatest at stations with the greatest metal enrichment and with the least dilution and flushing of wastes. A consistent seasonal pattern of fluctuation in Cu and Ag concentrations was evident in M. balthica at the metal-enriched station. These seasonal changes in tissue metal concentrations appeared to be affected by metal inputs, hydrologic processes that may affect both metal concentrations and bioavailability, and seasonal changes in the weight of the bivalve. The contributions of each of these interacting factors could not be determined quantitatively. At the metal-enriched station significant variation in the amplitude of seasonal fluctuations was also evident from year to year. Interpretation of metal concentrations in bivalves from estuaries will require careful consideration of the processes which affect metal dynamics in these complex environments. 相似文献
105.
Abstract Receptor-mediated stimulation of Dictyostelium cells by the aggregative chemoattractant cyclic AMP leads to a complex excitatory response resulting in chemotaxis and the synthesis and release of cyclic AMP as the relayed chemotactic signal. However, the mechanism of this stimulus-response coupling is not well understood. In this study, we show that a number of compounds, best known as inhibitors of cyclooxygenase activity in mammalian cells, prevent cyclic AMP receptor-mediated cell excitation and cyclic AMP accumulation in aggregation-competent Dictyostelium cells. These observations suggest that some eicosanoid-like compound(s) may be involved in stimulus-response coupling in this organism, as is the case in higher eukaryotic cells. 相似文献
106.
Synopsis Prespawning female dace were examined in 7 successive years; in 6 years mean egg size (mm3) and egg number were inversely related and hence the ovary weights of equivalent-sized females were constant. Fecundity increased logarithmically with fish length, and an index of reproductive effort (ovary weight ÷ length cubed) also increased. The number of eggs per gram of ovarian tissue decreased with fish length; this was because mean egg size (mm3) increased and not because of a change in the proportion of connective tissue in the ovary. But in 1977, both egg number and mean egg size were low, although very high somatic growth had occurred in the previous, very warm, summer of 1976. Eggs from different-sized female dace were artificially fertilized, and incubated at a constant temperature. Dry weights of larvae, egg dry weights, mean egg size and larval starvation times showed linear correlations with each other and with parental (female) lengths. The progeny from the very smallest parent died several days earlier than those from the other parents. Size-related predation rates may be of more consequence than starvation death in natural populations. The optimum position of dace along the continuum between many small eggs and fewer larger eggs may vary at different levels of reproductive effort. 相似文献
107.
Christopher P. Moorhouse Barry Halliwell Martin Grootveld John M.C. Gutteridge 《Biochimica et Biophysica Acta (BBA)/General Subjects》1985,843(3)
Co(II) ions react with hydrogen peroxide under physiological conditions to form a ‘reactive species’ that can hydroxylate aromatic compounds (phenol and salicylate) and degrade deoxyribose to thiobarbituric-acid-reactive material. Catalase decreases the formation of this species but superoxide dismutase or low concentrations of ascorbic acid have little effect. EDTA, present in excess over the Co(II), can accelerate deoxyribose degradation and aromatic hydroxylation. In the presence of EDTA, deoxyribose degradation by the reactive species is inhibited competitively by scavengers of the hydroxyl radical (OH), their effectiveness being related to their second-order rate constants for reaction with OH. In the absence of EDTA the scavengers inhibit only at much higher concentrations and their order of effectiveness is changed. It is suggested that, in the presence of EDTA, hydroxyl radical is formed ‘in free solution’ and attacks deoxyribose or an aromatic molecule. In the absence of EDTA, OH radical is formed in a ‘site-specific’ manner and is difficult to intercept by OH scavengers. The relationship of these results to the proposed ‘crypto OH’ radical is discussed. 相似文献
108.
109.
Christopher E. Taylor Philip W. Stashak George Caldes Benjamin Prescott B.J. Fowlkes Phillip J. Baker 《Cellular immunology》1984,83(1):26-33
Several lectins were tested for their capacity to alter the antibody response to type III pneumococcal polysaccharide (SSS-III). The antibody response was enhanced by concanavalin A (Con A), phytohemagglutinin (PHA), as well as lectins from Phytolacca americana (Pa-2), Pisum sativum (PSA), and Lens culinaris (LCH), when these lectins were given 2 days after immunization with SSS-III; however, suppression was obtained when Con A and Pa-2 were given at the time of immunization. By contrast the lectins from Vicia villosa (VVL) and Bauhinia purpurea (BPA) did not alter the antibody response. Since the lectins PSA and LCH bind to the same monosaccharide as Con A, whereas the other lectins bind to different monosaccharides, these findings indicate that there is no relationship between nominal monosaccharide specificity and the capacity to modulate the antibody response. Substantial increases in the magnitude of the IgG1 antibody response was noted after the administration of Con A whereas profound enhancement of IgG2a antibody response was noted after PHA was given. 相似文献
110.
Friedrich Christopher A. Chakravarti Shukti Ferrell Robert E. 《Biochemical genetics》1984,22(5-6):389-394
Biochemical Genetics - 相似文献