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81.
Edwin H. Bryant Lisa M. Meffert 《Evolution; international journal of organic evolution》1990,44(3):660-668
Multivariate phenotypic differentiation in eight morphometric traits was examined in bottleneck lines of the housefly initiated with one, four, or 16 pairs of flies from a natural outbred population. Differentiation was assessed using a Mahalanobis' distance metric in units of additive genetic variance and covariance estimated from the ancestral population (i.e., generalized genetic distance). This distance metric was partitioned into contributions of size and shape to total distance. Bottleneck lines of all sizes diverged significantly from the ancestral line, but the direction of these shifts differed among the lines of different initial founding size. Those populations founded with single pairs diverged from the ancestral line mostly in shape; the 16-pair lines differentiated almost entirely in size, and the four-pair lines were intermediate in the relative contribution of shape to differentiation from the control. Bottlenecks serve to alter the genetic relationships among traits within the derived populations and in doing so could promote speciation by permitting differentiation of the populations along evolutionary trajectories less accessible to the base population. 相似文献
82.
Occurrence of Nitrate Reductase and Molybdopterin in Xanthomonas maltophilia 总被引:1,自引:1,他引:0 下载免费PDF全文
Lisa M. Woodard Anthony R. Bielkie John F. Eisses Paul A. Ketchum 《Applied microbiology》1990,56(12):3766-3771
Fifteen of 23 ATCC strains and 2 of 9 clinical isolates of Xanthomonas maltophilia, all of which grew aerobically on ammonia, but not nitrate, as a sole nitrogen source, reduced nitrate to nitrite. X. maltophilia failed to grow anaerobically on complex medium with or without nitrate, so it is considered an obligate aerobe. Nitrate-reducing strains contained reduced methyl viologen nitrate reductase (MVH-NR) with specific activities ranging from 49.2 to 192 U mg of protein−1. Strain ATCC 17666 doubled its cell mass after 3 h of growth on nitrate broth under low aeration, possessed maximal MVH-NR activity, and converted the added nitrate to nitrite, which accumulated. Dissolved oxygen above 15% saturation greatly suppressed nitrite formation. All strains, except ATCC 14535, possessed between 0.25 and 5.05 pmol of molybdopterin mg of protein−1 as measured by the Neurospora crassa nit-1 assay. The molybdopterin activity in the soluble fraction sedimented as a single symmetrical peak with an s20,w of 5.1. Studies identified MVH-NR in selected strains as a membrane-bound protein. The deoxycholate-solubilized MVH-NR sedimented as a single peak in sucrose density gradients with an s20,w of 8.8. The MVH-NR of X. maltophilia has the physical characteristics of a respiratory nitrate reductase and may enable cells to use nitrate as an electron sink under semiaerobic conditions. 相似文献
83.
The possible contribution of pinon (Pinus edulis) seed to the diet of an Anasazi population is investigated using present data on seed productivity and archaeological data on resource use. Annual estimates of total productivity for a 135.7 sq km study area in Montezuma County, Colorado, vary by a factor of 141 in a sample spanning 5 yr. Trees greater than about 25 cm (basal diameter) are usually monoecious and produce significantly more cones per tree but fewer good seeds per cone than smaller, usually dioecious specimens. Archaeological data suggest that piñon seed was a relatively unimportant food item after the initial period of Anasazi colonization of the Dolores River valley about a.D. 600. Use of piñon seed as food was inversely related to degree of agricultural intensification and use of piñon for fuel. 相似文献
84.
Mouse submandibular epithelial cells can be grown in primary culture using the collagen gel matrix and a chemically defined medium consisting of insulin, transferrin, cholera toxin, and BSA (or FGF). Sustained cell growth leading to a 5–10-fold increase in cell number was observed in less than 2 weeks. In the presence of these additives, clumps of cells proliferate by extending ‘star-like’ projections into the matrix, resulting in three-dimensional outgrowths. The morphology of these outgrowths can be modulated to form a ‘cyst-like’ appearance by deleting BSA and adding cortisol to the basal medium containing insulin, transferrin, cholera toxin and FGF. In brief, a serum-free medium for sustained growth has been devised and a simple manipulation of supplements can modulate the three-dimensional colony morphology in the collagen gel matrix. Finally, the resulting outgrowths can produce epidermal growth factor (EGF) in response to dihydrotestosterone. 相似文献
85.
Chi promotes Rec-mediated recombination between phage lambda DNA and the homologous plasmid lambda dv. In the absence of Chi, some of the interactions splice lambda dv into lambda, whereas others patch information from lambda dv into lambda. When Chi is in the phage DNA, splices and patches are increased in frequency by the same factor. This result strengthens the analogy between Chi and recombination-promoting elements in fungi. It also rules out one model for the previously reported orientation dependence of Chi phenotype. 相似文献
86.
Lisa Balick Lloyd Elfner Jack May J. David Moore 《Applied psychophysiology and biofeedback》1982,7(4):499-520
Nine dysmenorrheic women were run in EMG and thermal biofeedback procedures with concurrent autogenic relaxation practice. Significant reductions in subjective estimates of symptomology associated with dysmenorrhea were noted in all subjects. EMG levels correlated positively with the reductions in symptoms. Thermal levels did not correlate with EMG. In fact no consistent patterns in thermal measures were noted. However, thermal biofeedback cannot be ruled out as an effective treatment for dysmenorrhea since reductions in symptoms occurred during thermal biofeedback training. Another significant aspect of the present study is the effectiveness of long treatment procedures. A six month period was employed and significant reductions in symptoms were noted following two months of biofeedback treatment. Finally, the importance of beginning biofeedback treatment prior to onset of menstrual symptoms is indicated. 相似文献
87.
Lisa Kunnath Joseph Locker 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1982,699(3):264-271
In the rat, differentiation and cell proliferation both affect DNA methylation. We studied 5-methylcytosine at the inner cytosine of the sequence C-C-G-G, a common methylation site, using endonuclease MspI (which cleaves C-C-G-G- and C-mC-G-G), and its isoschizomer HpaII (which cleaves only C-C-G-G). DNA from all tissues and cell lines studied was methylated at C-C-G-G, at levels ranging from 45 to 80%, but the methylation sites were not distributed uniformly. Our analysis suggests a model in which cells contain variable amounts of three DNA methylation states, averaging 30–40, 70–80 and 95–100% methylation, respectively. One biological parameter that alters methylation is the prolferative state of the cell. We observed that NRK, a non-transformed cell line, increased its DNA methylation from 45 to 67% when monolayer cultures became confluent and non-dividing. We also observed that a class of repetitive DNA was completely methylated in DNA from all sources except a transformed cell line. 相似文献
88.
Glutamine synthetase (GS) level is positively influenced by exogenously supplied sucrose in isolated pea roots (similarly as nitrate reductase - NR), glutamate dehydrogenase (GDH) level negatively. Comparison with previous results shows that GS level decreases more slowly than NR level when sucrose is omitted from the medium; the rate of changes in GS level corresponds rather to that in GDH level. The increase in GDH level in the tips of isolated roots cultivated in the medium lacking sucrose stops after approx. 24 h, but continues for at least 72 h in more mature root parts. GS level decreases during the first 24 h in the tips of isolated roots (compared with roots of intact seedlings) cultivated both with sucrose and without it (without sucrose more), however it again rises in the course of further cultivation with sucrose. The differences in GS and GDH levels caused by omission of sucrose are small in isolated roots from which root tips were removed, the difference in NR level in decapitated roots is similar to that found in isolated roots with root tips left. Decapitated isolated roots cultivated without sucrose contain higher amounts of soluble sugars than corresponding roots with root tips left. These facts are dismissed with regard to sugar consumption, transport, and compartmentalisation, and with respect to production in root tips and other plant parts of unknown compounds involved in GS and GDH regulation. The results obtained suggest that GDH functions in pea roots in the deaminating direction. 相似文献
89.
Thomas L. Steinacker Siu-Shing Wong Zsofia A. Novak Saroj Saurya Lisa Gartenmann Eline J.H. van Houtum Judith R. Sayers B. Christoffer Lagerholm Jordan W. Raff 《The Journal of cell biology》2022,221(9)
Centrioles duplicate once per cell cycle, but it is unclear how daughter centrioles assemble at the right time and place and grow to the right size. Here, we show that in Drosophila embryos the cytoplasmic concentrations of the key centriole assembly proteins Asl, Plk4, Ana2, Sas-6, and Sas-4 are low, but remain constant throughout the assembly process—indicating that none of them are limiting for centriole assembly. The cytoplasmic diffusion rate of Ana2/STIL, however, increased significantly toward the end of S-phase as Cdk/Cyclin activity in the embryo increased. A mutant form of Ana2 that cannot be phosphorylated by Cdk/Cyclins did not exhibit this diffusion change and allowed daughter centrioles to grow for an extended period. Thus, the Cdk/Cyclin-dependent phosphorylation of Ana2 seems to reduce the efficiency of daughter centriole assembly toward the end of S-phase. This helps to ensure that daughter centrioles stop growing at the correct time, and presumably also helps to explain why centrioles cannot duplicate during mitosis. 相似文献