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101.
Abstract Eight Nif− mutants of Azospirillum brasilense were obtained by N -nitrosoguanidine mutagenesis and isolated by growth on glutamate medium. Three of these mutants had no nitrogenase activity, possessed no nitrogenase structural proteins and were complemented by Klebsiella pneumoniae nifA . Evidence will be presented that one of these mutants is defective in a nifA type regulatory gene but the other two were also complemented by K. pneumoniae ntrC and may be ntrC− -type mutants. A fourth mutant was defective in the MoFe component protein of nitrogenase. 相似文献
102.
Patrice Allibert J.Martin Odom J.D. Wall P.M. Vignais 《FEMS microbiology letters》1984,23(2-3):221-226
Abstract Spontaneous nitrogenase-negative (Nif− mutants of Rhodopseudomonas capsulata were observed to accumulate with time in ammonium- or glutamate-limited chemostat cultures.
Nif− mutants were characterized by their inability to grow under N2 and to reduce acetylene or produce hydrogen gas when grown on glutamate. They lacked the nitrogenase structural proteins as evidenced by immunological techniques. On the other hand, no significant differences were found in the pathways of ammonia assimilation between the Nif− mutants and the wild-type strain. The Nif− mutants seem to result from a mutation in a regulatory gene. 相似文献
Nif
103.
104.
The suppressible eye color mutant purple (pr) of Drosophila melanogaster is known to be unable to synthesize a wild-type complement of pteridine eye pigments. This study measures the reduced levels of drosopterins, sepiapterin, and an unidentified presumed pteridine in pr and pr
bw. Pteridine analyses in double mutants combining pr with one of three other eye color mutants sepia, Henna-recessive3, and prune2, suggest that the metabolic block in pr occurs prior to sepiapterin biosynthesis. Measurements of GTP and GTP cyclohydrolase in pr showed wild-type levels and indicate the metabolic block in pr to be at one of the steps converting dihydroneopterin triphosphate to sepiapterin. Quantitation of pteridines in suppressed purple [su(s)
2; pr and pr; su(pr)
e3] shows restoration of pteridines to wild-type or nearly wild-type levels.T. G. W. is a predoctoral trainee supported by Grant GM 1974 from the National Institute of General Medical Sciences, National Institutes of Health.The Oak Ridge National Laboratory is operated by Union Carbide Corporation for the U.S. Energy Research and Development Administration. 相似文献
105.
Ade–H and ade–I are two auxotrophic mutants of Chinese hamster ovary (CHO-K1) cells which specifically require adenine as the purine source to grow. The enzymatic defects of these mutants were examined in cell-free extracts. It was found that ade–H did not have any detectable adenylosuccinate synthetase activity and ade–I was defective in the adenylosuccinate lyase enzyme. The relevance of adenine-requiring mutants to the study of the regulation of purine metabolism in mammalian cells is discussed.This work was supported by research grants from the National Institute of Aging (AG00029) and the National Foundation, March of Dimes (1-423), and by a contract from the Center for Toxicological Research, Food and Drug Administration (72-213). David Patterson is a recipient of a Research Career Development Award from the National Institute of Arthritis, Metabolic and Digestive Diseases (AM00044).Contribution (No. 218) from the Eleanor Roosevelt Institute for Cancer Research. 相似文献
106.
Nitrous acid (NA) induced mutations efficiently in mitDNA, conferring resistance to erythromycin and weakly induces mit- mutations. In some strains of yeast it also enhanced rho- mutations. The frequencies of nuclear and mitochondrial mutations induced with NA are compared. 相似文献
107.
The initiation of sporangiophores of Phycomyces was analyzed under oxygen-limiting conditions. Mutants lacking -carotene have a higher oxygen threshold than the wild type depending on the residual amount of -carotene. The supersensitivity to low oxygen tension is specific for sporangiophore initiation and can be suppressed by addition of either retinal, retinol or retinol acetate to the medium. It is suggested that retinol is a natural regulator of differentiation in Phycomyces. 相似文献
108.
Chromatography of soluble polyphenols of p-fluorophenylalanine-sensitive and -resistant tobacco cells revealed that the 10-fold increased level found in the resistant line was largely due to the accumulation of two unidentified polyphenols. The uptake of Phe-[U-14C] and Tyr-[U-14C] by the resistant line was ca 10 % that by the sensitive line. About 90 % of the phenylalanine-[14C] which was taken up by both cell lines could be accounted for as free phenylalanine in protein, soluble polyphenols or CO2. The fate of Tyr-[14C] was similar to that of phenylalanine except that the incorporation was into insoluble polymeric forms of polyphenols rather than into soluble polyphenols. The resistant line incorporated 9-times more phenylalanine-[14C] into soluble polyphenols than did the sensitive line. The different 14C-aromatic amino acid accumulation and incorporation patterns noted with the two cell lines indicates that there are different active pools. Differential uptake rates by the two cell lines might affect the distribution of the absorbed amino acid among the different pools. 相似文献
109.
Studies of chloroplast development in four maize mutants defective in chlorophyll biosynthesis 总被引:3,自引:0,他引:3
Four mutants of maize (Zea mays L.) defective in chlorophyll biosynthesis have been analyzed with regard to the sites of their lesions and their effects on chloroplast development. Two yellow mutants, which accumulate no detectable porphyrin precursors when grown in darkness, are defective in the conversion of protoporphyrin IX to magnesium protoporphyrin. Etioplasts of these mutants may develop elaborate lamellar membrane systems, but prolamellar bodies are never observed. Two mutants, which are necrotic when grown under illumination, develop normal (non-necrotic) leaf tissue in the dark and accumulate a small amount of magnesium protoporphyrin monomethyl ester, corresponding approximately to the amount of protochlorophyllide accumulated by normal plants. The etioplasts of these mutants contain noncrystalline bodies. The implications of these observations with respect to chloroplast development are discussed.Journal Paper No. J-9136 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa Project No. 2035 相似文献
110.
Rockford K. Draper Daniel Chin Lisa Stubbs Melvin I. Simon 《Journal of cellular biochemistry》1978,9(1):47-55
Concanavalin A, wheat germ agglutinin and the ovalbumin glycopeptide are all inhibitors of the cytotoxic effect of diphtheria toxin on Chinese hamster cells. Ovalbumin glycopeptide loses its inhibitory property after treatment with β-N-acetylglucosaminidase. This demonstrates the importance of the glycopeptide structure for the mechanism of inhibition. The glycopeptide may be a toxin cell-surface receptor analogue. Diphtheria toxin-resistant mutants were isolated in order to search for cells that might have an altered toxin receptor. One mutant was 10-to 15-fold more resistant to diphtheria toxin than wild-type cells when protein synthesis was measured as a function of toxin concentration. However, when protein synthesis was measured as a function of time at a high toxin concentration, the time before onset of inhibition was identical in the mutant and wild-type cells. We present evidence indicating that the resistance of this mutant can be accounted for by a decreased affinity of toxin for a cell-surface receptor. 相似文献