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31.
Cultures of adult mouse-lung fibroblasts have been treated by series of strong and weak muta-carcinogens. Unscheduled DNA synthesis has been measured by quantitative autoradiography using automatic image analysis. Some of the muta-carcinogens (AFB1, DMN, B(a)P, DMBA, MNNG, 4-NQO) yielded a measurable UDS response, whereas others (2-AA, AFB2, B(e)P, ICR-191) usually known as weak carcinogens, gave no response. The response was not improved by addition of liver S9. This shows that mouse-lung fibroblasts possess their own but limited metabolic activation systems. 相似文献
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R. Rodicio H. -D. Schmitt J. Heinisch F. K. Zimmermann 《Molecular & general genetics : MGG》1984,197(3):491-496
Summary Yeast DNA pools were prepared by ligating partial Sau3A genomic digests from strains carrying various MAL genes into the BamHI site of the yeast-Escherichia coli shuttle vector YRp7. They were used to transform recipient yeast strains that could not utilize maltose since they lacked a classical MAL gene. Transformants were obtained that could use maltose and also formed normal levels of maltase. They were unstable. They would lose the selective marker TRP1 of YRp7 alone, together with the ability to utilize maltose or only the ability to utilize maltose. The insertion of one of the plasmids was used as a hybridization probe for the others and found to share homologous sequences with all. They were then shown to contain the replication origin of the yeast 2 m circle plasmid and additional genomic digests of total yeast DNA. They hybridized at various degrees of efficiency with several bands, indicating that they were part of a family of repeated sequences. Apparently, it was the combination of the replication origin of the 2 m circles with the additional sequences that promoted maltose utilization. 相似文献
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I. Breitenbach-Schmitt J. Heinisch H. D. Schmitt F. K. Zimmermann 《Molecular & general genetics : MGG》1984,195(3):530-535
Summary Mutants of Saccharomyces cerevisiae without detectable phosphofructokinase activity were isolated. They were partly recessive and belonged to two genes called PFK1 and PFK2. Mutants with a defect in only one of the two genes could not grow when they were transferred from a medium with a nonfermentable carbon source to a medium with glucose and antimycin A, an inhibitor of respiration. However, the same mutants could grow when antimycin A was added to such mutants after they had been adapted to the utilization of glucose. Double mutants with defects in both genes could not grow at all on glucose as the sole carbon source. Mutants with a single defect in gene PFK1 or PFK2 could form ethanol on a glucose medium. However, in contrast to wild-type cells, there was a lag period of about 2 h before ethanol could be formed after transfer from a medium with only nonfermentable carbon sources to a glucose medium. Wild-type cells under the same conditions started to produce ethanol immediately. Mutants with defects in both PFK genes could not form ethanol at all. Mutants without phosphoglucose isomerase or triosephosphate isomerase did not form ethanol either. Double mutants without phosphofructokinase and phosphoglucose isomerase accumulated large amounts of glucose-6-phosphate on a glucose medium. This suggested that the direct oxidation of glucose-6-phosphate could not provide a bypass around the phosphofructokinase reaction. On the other hand, the triosephosphate isomerase reaction was required for ethanol production. Experiments with uniformly labeled glucose and glucose labeled in positions 3 and 4 were used to determine the contribution of the different carbon atoms of glucose to the fermentative production of CO2. With only fermentation operating, only carbon atoms 3 and 4 should contribute to CO2 production. However, wild-type cells produced significant amounts of radioactivity from other carbon atoms and pfk mutants generated CO2 almost equally well from all six carbon atoms of glucose. This suggested that phosphofructokinase is a dispensable enzyme in yeast glycolysis catalyzing only part of the glycolytic flux. 相似文献
34.
Synopsis Black surfperch, Embiotoca jacksoni, and striped surfperch, Embiotoca lateralis, coexisted along steep sloping rocky habitats at Santa Cruz Island, California. The range of depths occupied (to 15 m) was characterized by a strong gradient in abundance of prey and a changing mosaic of substrate types from which surfperch harvested food. Availability of prey and diversity of benthic substrates were greatest in shallowest areas and both declined with increasing depth. Individuals of both surfperch species were residential within a narrow range of depths, with the result that different segments of their populations were consistently exposed to different foraging environments. These two phenomena (residential behavior combined with a gradient in availability of resources) resulted in variation in foraging behaviors and diets among individuals that resided at different depths. The pattern of within-population variation differed between the surfperch species. Black surfperch individuals achieved similar taxonomic diets and expended similar foraging effort at all depths, but deep-water foragers captured much less prey biomass per unit effort. The taxonomic composition of striped surfperch diets differed among depths, and although similar amounts of prey biomass were captured everywhere, individuals in deep areas expended much greater effort to obtain that level of food return. For both species, habitat profitability (food return to foraging effort) declined with depth. The difference in habitat profitability appeared to influence fitness components of both surfperches. Individuals occupying deep habitats were about 5% shorter in standard length than conspecifics of the same chronological age living in shallow areas; the disparity in body size resulted in an estimated difference in clutch size of 10–18%. 相似文献
35.
W P Diver J Grinsted D C Fritzinger N L Brown J Altenbuchner P Rogowsky R Schmitt 《Molecular & general genetics : MGG》1983,191(2):189-193
DNA sequences that encode the tnpR genes and internal resolution (res) sites of transposons Tn21 and Tn501, and the res site and the start of the tnpR gene of Tn1721 have been determined. There is considerable homology between all three sequences. The homology between Tn21 and Tn501 extends further than that between Tn1721 and Tn501 (or Tn21), but in the homologous regions, Tn1721 is 93% homologous with Tn501, while Tn21 is only 72-73% homologous. The tnpR genes of Tn21 and Tn501 encode proteins of 186 amino acids which show homology with the tnpR gene product of Tn3 and with other enzymes that carry out site-specific recombination. However, in all three transposons, and in contrast to Tn3, the tnpR gene is transcribed towards tnpA gene, and the res site is upstream of both. The res site of Tn3 shows no obvious homology with the res regions of these three transposons. Just upstream of the tnpR gene and within the region that displays common homology between the three elements, there is a 50 bp deletion in Tn21, compared to the other two elements. A TnpR- derivative of Tn21 was complemented by Tn21, Tn501 and Tn1721, but not by Tn3. 相似文献
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Numerical taxonomy of Nocardia 总被引:7,自引:0,他引:7