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91.
Synthesis of deoxyribomononucleotides in Mollicutes: dependence on deoxyribose-1-phosphate and PPi. 总被引:5,自引:4,他引:1
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Cell extracts of Acholeplasma laidlawii B-PG9, Acholeplasma morum S2, Mycoplasma capricolum 14, and Mycoplasma gallisepticum S6 were examined for 37 cytoplasmic enzyme activities involved in the salvage and biosynthesis of purines. All of these organisms had adenine phosphoribosyltransferase activity (EC 2.4.2.7) and hypoxanthine phosphoribosyltransferase activity (EC 2.4.2.8). All of these organisms had purine-nucleoside phosphorylase activity (EC 2.4.2.1) in the synthetic direction using ribose-1-phosphate (R-1-P) or deoxyribose-1-phosphate (dR-1-P); this activity generated ribonucleosides or deoxyribonucleosides, respectively. The pyrimidine nucleobase uracil could also be ribosylated by using either R-1-P or dR-1-P as a donor. The synthesis of deoxyribonucleosides from nucleobases and dR-1-P has been reported from only one other procaryote, Escherichia coli (L. A. Mason and J. O. Lampen, J. Biol. Chem. 193:539-547, 1951). The reverse of this phosphorylase reaction is more widely known, and we found such activity in all mollicutes studied. Some Acholeplasma species but not the Mycoplasma species can phosphorylate deoxyribonucleosides to deoxyribomononucleotides by a PPi-dependent deoxyribonucleoside kinase activity, which was first reported in this group for the ribose analogs (V. V. Tryon and J. D. Pollack, Int. J. Syst. Bacteriol. 35:497-501, 1985). This is the first report of PPi-dependent purine deoxyribonucleoside kinase activity. An ATP-dependent purine deoxyribonucleoside kinase activity is known only in salmon milt extracts (H. L. A. Tarr, Can. J. Biochem. 42:1535-1545, 1964). Deoxyribomononucleotidase activity was also found in cytoplasmic extracts of these mollicutes. This is the first report of deoxyribomononucleotidase activity. 相似文献
92.
The Absence of Somatic Effects of P-M Hybrid Dysgenesis in DROSOPHILA MELANOGASTER 总被引:3,自引:0,他引:3
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M. Catharine McElwain 《Genetics》1986,113(4):897-918
The wings and abdomens of dysgenic and nondysgenic control flies were scored for the presence of clones of cells mutant for first and third chromosome markers. These exceptional clones can arise from mitotic recombination, de novo mutation or deletion, and P-M hybrid dysgenesis has been shown to increase the frequency of parallel processes occurring in germ-line cells. Particular attention was given to careful genetic and molecular characterization of all stocks and to providing adequate and appropriate controls so that even very small increases in somatic clone frequency due to P-M hybrid dysgenesis would be detected. No difference was found in the frequency, size distribution or anatomical distribution of mutant somatic clones correlated to hybrid dysgenesis, confirming previous indications. The potential adaptive significance of a germ-line restriction of P-M hybrid dysgenesis is discussed. 相似文献
93.
94.
Fitness effects of amino acid replacements in the beta-galactosidase of Escherichia coli 总被引:7,自引:1,他引:6
Two genetic procedures were used to obtain amino acid replacements in the
lacZ-encoded beta-galactosidase in Escherichia coli. Amino acid
replacements could be obtained without regard to their effects on lactase
activity by selecting spontaneous mutations that relieved the strong
polarity of six nonsense mutations. When streaked on MacConkey- lactose
indicator plates, approximately 75% of these mutants gave strong red
lactose-fermenting colonies, and 25% gave white nonfermenting colonies.
Mutants from 11 other nonsense codons were isolated directly using
MacConkey-lactose indicator plates, on which positive color indication
requires only 0.5% of the wildtype lactase activity. Among the total of 17
codons, 25 variant beta-galactosidases were identified using
electrophoresis and thermal denaturation studies. The fitness effects of
these variant beta-galactosidases were determined using competition
experiments conducted with lactose as the sole nutrient limiting the growth
rate in chemostat cultures. Three of the replacements were deleterious, one
was selectively advantageous, and the selective effects of the remaining 21
were undetectable under conditions in which the smallest detectable
selection coefficient was approximately 0.4%/generation.
相似文献
95.
We have isolated a nuclear mutant (tsp-1) of Chlamydomonas reinhardtii which is resistant to thiostrepton, an antibiotic that blocks bacterial protein synthesis. The tsp-1 mutant grows slowly in the presence or absence of thiostrepton, and its chloroplast ribosomes, although resistant to the drug, are less active than chloroplast ribosomes from the wild type. Chloroplast ribosomal protein L-23 was not detected on stained gels or immunoblots of total large subunit proteins from tsp-1 probed with antibody to the wild-type L-23 protein from C. reinhardtii. Immunoprecipitation of proteins from pulse-labeled cells showed that tsp-1 synthesizes small amounts of L-23 and that the mutant protein is stable during a 90 min chase. Therefore the tsp-1 phenotype is best explained by assuming that the mutant protein synthesized is unable to assemble into the large subunit of the chloroplast ribosome and hence is degraded over time. L-23 antibodies cross-react with Escherichia coli r-protein L11, which is known to be a component of the GTPase center of the 50S ribosomal subunit. Thiostrepton-resistant mutants of Bacillus megaterium and B. subtilis lack L11, show reduced ribosome activity, and have slow growth rates. Similarities between the thiostreptonresistant mutants of bacteria and C. reinhardtii and the immunological relatedness of Chlamydomonas L-23 to E. coli L11 suggest that L-23 is functionally homologous to the bacterial r-protein L11. 相似文献
96.
Bullard SA Ruiz CF McElwain A Murray MJ Borucinska JD Benz GW 《The Journal of parasitology》2012,98(2):333-340
Eggs of Huffmanela cf. carcharhini from the skin of an aquarium-held, juvenile sandbar shark, Carcharhinus plumbeus , from the Pacific Ocean were studied using light and scanning electron microscopy. Grossly, eggs imparted a scribble-like skin marking approximately 130 × 60 mm on the right side of the shark's snout adjacent to its eye and nostril. Fresh (unfixed) eggs were elliptical, 75-95 μm long (xˉ = 85 μm, SD = ±4.5; n = 75), 48-63 μm wide (53 ± 3.4; 75), 8-10 μm in shell thickness (9 ± 1.3; 27), 45-68 μm in vitelline mass length (52 ± 6.9; 8); had a smooth shell surface and nonprotruding polar plugs 8-13 μm wide (10 ± 1.5; 73); lacked thin filaments, superficial envelope, and shell spines; sank in 35 ppt artificial seawater; and did not spontaneously hatch after 12 hr in 35 ppt artificial seawater. Formalin-fixed eggs measured 193 days postfixation were 75-95 μm long (84 ± 3.9; 150), 45-60 μm wide (50 ± 2.2; 150), 5-10 μm in shell thickness (8 ± 1.2; 87), 45-60 μm in vitelline mass length (51 ± 3.0; 92), and 30-40 μm in vitelline mass width (33 ± 2.0; 84), and had nonprotruding polar plugs that were 10-15 μm long (11 ± 1.4; 93) and 8-10 μm wide (9 ± 1.1; 108). Forcibly hatched first-stage larvae (unfixed) were filiform, 188-273 μm long (212 ± 25.5; 13), 8-13 μm wide (10 ± 1.2; 13), and had fine transverse striations. Eggs infected the epidermis only. Histology revealed intra-epithelial inflammation with eosinophilic granulocytes and hyperplasia, plus dermal lymphofollicular hyperplasia associated with the infection. The eggs of H. cf. carcharhini likely undergo considerable ex utero development before being sloughed (unhatched) from the host, along with epidermal cells. 相似文献
97.
The interpretation of biotic changes in the geological past relies on the assumption that samples from different time intervals represent an equivalent suite of natural sampling conditions. As a result, detailed investigations of taphonomic regimes during intervals of major biotic upheaval, such as mass extinctions, are crucial. In this paper, we have used variations in the frequency of chemical and mechanical sporomorph (pollen and spore) damage as a guide to taphonomic regimes across the Triassic–Jurassic mass extinction (Tr-J; ∼201.3 Ma) at a boundary section at Astartekløft, East Greenland. We find that the frequency of sporomorph damage is extremely variable in samples from this locality. This likely reflects a combination of taxon-specific susceptibility to damage and the mixing of sporomorphs from a mosaic of environments and taphonomic regimes. The stratigraphic interval containing evidence of plant extinction and compositional change in the source vegetation at Astartekløft is not marked by a consistent rise or fall in the frequency of sporomorph damage. This indicates that natural taphonomic regimes did not shift radically during this critical interval. We find no evidence of a consistent relationship between the taxonomic richness of sporomorph assemblages and the frequency of damage among sporomorphs at Astartekløft. This indicates that previously reported patterns of sporomorph richness across the Tr-J at this locality are likely to be robust. Taken together, our results suggest that the patterns of vegetation change at Astartekløft represent a real biological response to environmental change at the Tr-J. 相似文献
98.
Introns and reading frames: correlation between splicing sites and their codon positions 总被引:4,自引:1,他引:3
Computer analyses of the entire GenBank database were conducted to examine
correlation between splicing sites and codon positions in reading frames.
Intron insertion patterns (i.e., splicing site locations with respect to
codon positions) have been analyzed for all of the 74 codons of all the
eukaryote taxonomic groups: primates, rodents mammals, vertebrates,
invertebrates, and plants. We found that reading frames are interrupted by
an intron at a codon boundary (as opposed to the middle of a codon)
significantly more often than expected. This observation is consistent with
the exon shuffling hypothesis, because exons that end at codon boundaries
can be concatenated without causing a frame shift and thus are
evolutionarily advantageous. On the other hand, when introns interrupt at
the middles of codons, they exist in between the first and second bases
much more frequently than between the second and third bases, despite the
fact that boundaries between the first and second bases of codons are
generally far more important than those between the second and third bases.
The reason for this is not clear and yet to be explained. We also show that
the length of an exon is a multiple of 3 more frequently than expected.
Furthermore, the total length of two consecutive exons is also more
frequently a multiple of 3. All the observations above are consistent with
results recently published by Long, Rosenberg, and Gilbert (1995).
相似文献
99.
Olivares-Fuster O Bullard SA McElwain A Llosa MJ Arias CR 《Diseases of aquatic organisms》2011,96(3):221-227
The adhesion dynamics of Flavobacterium columnare to fish tissues were evaluated in vivo by immersion challenge followed by bacterial plate count and confirmatory observations of gill-adhered bacterial cells using scanning electron microscopy. Adhesion of F. columnare genomovar I (ARS-1) and II (BGFS-27) strains to skin and gill of channel catfish Ictalurus punctactus and gill of zebrafish Danio rerio was compared. At 0.5 h post-challenge, both strains adhered to gill of channel catfish at comparable levels (10(6) colony forming units [CFU] g(-1)), but significant differences in adhesion were found later in the time course. Channel catfish was able to effectively reduce ARS-1 cells on gill, whereas BGFS-27 persisted in gill beyond the first 24 h post-challenge. No significant difference was found between both strains when adhered to skin, but adhered cell numbers were lower (10(3) CFU g(-1)) than those found in gill and were not detectable at 6 h post-challenge. Adhesion of BGFS-27 cells to gill of zebrafish also occurred at high numbers (> 10(6) CFU g(-1)), while only < 10(2) CFU g(-1) of ARS-1 cells were detected in this fish. The results of the present study show that particular strains of F. columnare exhibit different levels of specificity to their fish hosts and that adhesion to fish tissues is not sufficient to cause columnaris disease. 相似文献
100.
Clifford DL Folmes D Kent Arrell Jelena Zlatkovic-Lindor Almudena Martinez-Fernandez Carmen Perez-Terzic Timothy J Nelson Andre Terzic 《Cell cycle (Georgetown, Tex.)》2013,12(15):2355-2365
Nuclear reprogramming resets differentiated tissue to generate induced pluripotent stem (iPS) cells. While genomic attributes underlying reacquisition of the embryonic-like state have been delineated, less is known regarding the metabolic dynamics underscoring induction of pluripotency. Metabolomic profiling of fibroblasts vs. iPS cells demonstrated nuclear reprogramming-associated induction of glycolysis, realized through augmented utilization of glucose and accumulation of lactate. Real-time assessment unmasked downregulated mitochondrial reserve capacity and ATP turnover correlating with pluripotent induction. Reduction in oxygen consumption and acceleration of extracellular acidification rates represent high-throughput markers of the transition from oxidative to glycolytic metabolism, characterizing stemness acquisition. The bioenergetic transition was supported by proteome remodeling, whereby 441 proteins were altered between fibroblasts and derived iPS cells. Systems analysis revealed overrepresented canonical pathways and interactome-associated biological processes predicting differential metabolic behavior in response to reprogramming stimuli, including upregulation of glycolysis, purine, arginine, proline, ribonucleoside and ribonucleotide metabolism, and biopolymer and macromolecular catabolism, with concomitant downregulation of oxidative phosphorylation, phosphate metabolism regulation, and precursor biosynthesis processes, prioritizing the impact of energy metabolism within the hierarchy of nuclear reprogramming. Thus, metabolome and metaboproteome remodeling is integral for induction of pluripotency, expanding on the genetic and epigenetic requirements for cell fate manipulation. 相似文献