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141.
Revertants and Secondary arom-2 Mutants Induced in Non-Complementing Mutants in the arom Gene Cluster of Neurospora Crassa 总被引:7,自引:0,他引:7
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Extensive genetical and biochemical studies have been performed with revertants and secondary arom-2 mutants induced in two different primary non-complementing mutants which map within the arom gene cluster of Neurospora crassa. These studies indicate that mutant M54 but not M25 can revert by super-suppressor mutations in unlinked genes, thus confirming previous evidence that M54 contains a nonsense codon. At least three new super suppressors of M54 have been detected. All four super suppressors (including one previously detected) when combined with M54 result in high levels of all five of the arom enzymic activities in the form of arom multienzyme complexes very similar to (but not necessarily identical with) that in wild type (WT).-Evidence has also been obtained that the two non-complementing mutants can yield revertants which appear to result from true back mutations and produce arom aggregates essentially indistinguishable from that of WT. In addition, M25, but not M54, when plated on quinic acid yields revertants (secondary mutants) some of which are phenotypically indistinguishable from arom-2 primary mutants and others of which, although also mapping within the arom-2 gene, exhibit unusual properties. Genetic evidence indicates that the M25 secondary mutants are localized within the arom-2 gene, but that they arise from mutational events more complex than ones resulting in single base pair changes in the M25 codon.-The recovery of secondary arom-2 mutants as revertants of non-complementing arom mutants provides strong evidence, independent of earlier recombination data, that non-complementing arom mutants are located within the arom-2 structural gene of the arom gene cluster. In addition, the occurrence and characteristics of these secondary arom-2 mutants provide strong evidence, independent of the results with nonsense suppressors, that the arom gene cluster is transcribed, beginning with the arom-2 gene, as a single polycistronic messenger ribonucleic acid (mRNA) molecule which is subsequently translated into the arom multienzyme complex. 相似文献
142.
Mary Callaghan Rose Robert W. Henkens 《Biochimica et Biophysica Acta (BBA)/General Subjects》1974,372(2):426-435
Stability constants of sodium and potassium complexes of valinomycin in some alcohols and water—organic solvent mixtures have been determined by titration, using circular dichroism to monitor complex formation. Constants range from 101 to 106 M−1. Stability of the potassium and sodium complexes increases with decreasing dielectric constant, but the ratio of the constants remains about 103–104. As others have shown, a similar selectivity for K+ is observed in a number of other types of measurements involving valinomycin. These include the permeability and conductance ratios which characterize the selectivity of cation transport through membranes and the ratio of salt extraction equilibrium constants. On the basis of data presented here, and elsewhere, it is suggested that conformational constraints within the depsipeptide part of the complexes aid ion selectivity and that differences in cation solvation and carbonyl ligand binding energies make an important, roughly equal, contribution. 相似文献
143.
144.
Mary J. Kurtz Peter Polgar Linda Taylor Alexander M. Rutenburg 《The Biochemical journal》1974,142(2):339-344
Inhibition of growth and DNA synthesis was observed in WI 38 cells incubated with 8-methylthioadenosine 3':5'-cyclic monophosphate or prostaglandin E(1). The effect of both compounds on cell growth was reversible. On removal of these compounds from culture media the cells initiated DNA synthesis and divided. In addition, prostaglandin E(1) stimulated cyclic AMP formation in these cells to over 40 times the normal basal value. The increase in cyclic AMP concentration in WI 38 cells after addition of prostaglandin E(1) showed a marked variation. Cells that had recently been treated with trypsin and plated at a lower cell density exhibited a smaller response to addition of prostaglandin E(1) than cells that had divided and reached confluence. 相似文献
145.
Mary T. Kalin Arroyo 《Brittonia》1973,25(2):177-191
Limnanthes floccosa Howell is a variable autogamous species of recent origin. The phenetic relationships of a large number of populations ofL. floccosa were studied using taximetric techniques. Five subspecies are recognized inL. floccosa on the basis of the taximetric results.Limnanthes floccosa ssp.californica andL. floccosa ssp.grandiflora are described as new, andL. floccosa ssp.pumila andL. floccosa ssp.bellingeriana are proposed as new combinations. Aspects of autogamy responsible for the highly discrete pattern of variation inL. floccosa are discussed. 相似文献
146.
Comparison of Undefined Medium and Its Dialyzable Fraction for Growth of Mycoplasma 总被引:11,自引:3,他引:8
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In examining the medium used in cultivation of Mycoplasma for deoxyribonucleic acid isolation, it was found that an aggregate was present which sedimented with the organisms and which was ethyl alcohol-precipitated during deoxyribonucleic acid purification. To eliminate the contaminating material, a method was devised to obtain only the dialyzable constituents of the medium. This report describes the preparation of a dialysate of soy peptone-yeast extract. The medium, obtained by immersion of the encased dehydrated ingredients in sodium chloride solution for 5.5 hr at approximately 80 C, has been employed as the basal medium for cultivation of a number of Mycoplasma species. Comparative growth curves of two saprophytic strains and two parasitic species indicated that multiplication in dialysate, with suitable supplement, followed the pattern typical of the common eubacteria. Thus, by elimination of the sediment which occurred in nondialyzed medium, Mycoplasma could be concentrated without concomitant accumulation of contaminating macromolecules. 相似文献
147.
The deoxyribonucleic acid homologies of Mycoplasma laidlawii type A and type B, M. pulmonis (#47 and #63), and M. hominis were determined by membrane methodology. The homology data revealed a difference in genome size between M. laidlawii type A and type B. This difference also held with stringent conditions of annealing (high temperature). Little or negligible homology was shown to exist between the M. laidlawii strains type A and type B and M. pulmonis strains 47 and 63 and M. hominis. M. hominis showed less than 10% homology to the M. pulmonis and M. laidlawii strains. Neither of the M. laidlawii strains showed more than 2% annealing to the M. pulmonis strains. Reaction rate studies are suggested as a means of demonstrating the phylogenetic relationship between the Mycoplasma and other microorganisms. 相似文献
148.
Summary Nitrogen deficient Anacystis nidulans contained normal levels of chlorophyll-a and carotenoids but did not contain any phycocyanin. These organisms also contained large amounts of polysaccharide. The addition of nitrate to a deficient culture resulted in the recovery of normal pigmentation over a period of several hours.The relation between these changes and growth was established by a kinetic study of the changes in cell composition during pigment loss and recovery. Loss of phycocyanin commenced with the cessation of growth due to nitrogen limitation and was complete after 15 hours. In contrast there were only minor changes in chlorophyll-a and carotenoid. After growth had ceased polysaccharide continued to increase and viability dropped sharply although total cell counts did not change. These trends were reversed by the addition of nitrate to deficient cultures. Phycocyanin was detected after a short lag and normal levels of phycobiliprotein were present within 8 hours. Cell division did not begin until normal levels of phycocyanin had been restored. During the recovery of normal pigmentation there was a decrease in reducing sugar content and a sharp rise in viability. Qualitative studies with 9 additional blue-green algae suggest that loss of phycocyanin is a characteristic feature of nitrogen deficiency in blue-green algae. 相似文献
149.
Studies have been made of marrow restoration after localized depletion of the rabbit femur by dextran perfusion. Restoration was shown to involve an initial period of reorganization which blends with a more prolonged period of hemic cell repopulation. Cellularity returned to normal levels by 35 days, the recovery of myeloid cells being somewhat more rapid than that of the erythroid elements. In either case, the evolution of immature hemic cells was soon followed by the appearance of more mature forms even at the earliest stages of marrow repopulation. 3H-TdR uptake per cell increased rapidly to a level approximately twice normal after the first week. The augmented incorporation of thymidine, revealed by scintillation spectrometry and confirmed upon autoradiography, was shown to be due to an increase in DNA synthesis rate as well as in the fraction of participating cells. It is suggested that the enhanced cell production is brought about by a decrease in the proliferative cell cycle and an increase in the growth fraction. The origin of the repopulating cells remains a moot point. Cell migration from the epiphyseal marrow is apparently not involved. Irrespective of the source of stem-type cells, the stimulus for regeneration appears to be locally determined. 相似文献
150.
Two Additional Salmonella Serotypes: Salmonella enteritidis Ser 58:a:- and Salmonella enteritidis Ser 44Z36, Z38:-
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Mary M. Ball William J. Martin Ronald M. Wood Catherine E. Powers 《Applied microbiology》1969,17(6):921-922
The antigenic compositions of two additional Salmonella serotypes isolated from the feces of man were determined to be 58:a:- and 44:Z(36), Z(38)-. 相似文献