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1.
Hardies SC; Martin SL; Voliva CF; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1986,3(2):109-125
2.
Protein degradation and protease activity during the late cycle of Blastocladiella emersonii 总被引:9,自引:3,他引:6
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Analysis of protein degradation during the life cycle of Blastocladiella emersonii showed that (i) protein degradation is especially high during two phases of differentiation (sporulation, 12%/h and germination, 5%/h) in contrast with a much smaller degradation rate in the other phases (growth and zoospores, less than 1%/hr); (ii) protein degradation during germination in growth medium, as well as most of the germination process, is quantitatively unaffected by cycloheximide; (iii) a caseinolytic protease (pH optimum 5.5, apparent molecular weight 55,000 to 60,000) is present in extracts of zoospores and germinating cells; (iv) this protease activity is very low (perhaps absent) in extracts of late growth phase cells, but reappears during induced sporulation; (v) a different class of caseinolytic protease activity (pH optima 7 and 10; apparent molecular weight 25,000 to 30,000) is found in cellular extracts of late growth phase and early phases of sporulation; (vi) the latter class of enzyme activity is released into the medium during later phases of sporulation and is replaced in the cells by the former class. Speculations as to the roles of protein degradation in cell differentiation are discussed. 相似文献
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6.
A major difference between the divergence patterns within the lines-1 families in mice and voles 总被引:3,自引:0,他引:3
Vanlerberghe F; Bonhomme F; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1993,10(4):719-731
L1 retroposons are represented in mice by subfamilies of interspersed
sequences of varied abundance. Previous analyses have indicated that
subfamilies are generated by duplicative transposition of a small number of
members of the L1 family, the progeny of which then become a major
component of the murine L1 population, and are not due to any active
processes generating homology within preexisting groups of elements in a
particular species. In mice, more than a third of the L1 elements belong to
a clade that became active approximately 5 Mya and whose elements are >
or = 95% identical. We have collected sequence information from 13 L1
elements isolated from two species of voles (Rodentia: Microtinae: Microtus
and Arvicola) and have found that divergence within the vole L1 population
is quite different from that in mice, in that there is no abundant
subfamily of homologous elements. Individual L1 elements from voles are
very divergent from one another and belong to a clade that began a period
of elevated duplicative transposition approximately 13 Mya. Sequence
analyses of portions of these divergent L1 elements (approximately 250 bp
each) gave no evidence for concerted evolution having acted on the vole L1
elements since the split of the two vole lineages approximately 3.5 Mya;
that is, the observed interspecific divergence (6.7%-24.7%) is not larger
than the intraspecific divergence (7.9%-27.2%), and phylogenetic analyses
showed no clustering into Arvicola and Microtus clades.
相似文献
7.
A simple mathematical model of the interaction between intracranial pressure and cerebral hemodynamics 总被引:6,自引:0,他引:6
Ursino, Mauro, and Carlo Alberto Lodi. A simplemathematical model of the interaction between intracranial pressure andcerebral hemodynamics. J. Appl.Physiol. 82(4): 1256-1269, 1997.A simplemathematical model of intracranial pressure (ICP) dynamics oriented toclinical practice is presented. It includes the hemodynamics of thearterial-arteriolar cerebrovascular bed, cerebrospinal fluid (CSF)production and reabsorption processes, the nonlinear pressure-volumerelationship of the craniospinal compartment, and a Starling resistormechanism for the cerebral veins. Moreover, arterioles are controlledby cerebral autoregulation mechanisms, which are simulated by means ofa time constant and a sigmoidal static characteristic. The model isused to simulate interactions between ICP, cerebral blood volume, andautoregulation. Three different related phenomena are analyzed: thegeneration of plateau waves, the effect of acute arterial hypotensionon ICP, and the role of cerebral hemodynamics during pressure-volume index (PVI) tests. Simulation results suggest the following:1) ICP dynamics may become unstablein patients with elevated CSF outflow resistance and decreasedintracranial compliance, provided cerebral autoregulation is efficient.Instability manifests itself with the occurrence of self-sustainedplateau waves. 2) Moderate acutearterial hypotension may have completely different effects on ICP,depending on the value of model parameters. If physiological compensatory mechanisms (CSF circulation and intracranial storage capacity) are efficient, acute hypotension has only negligible effectson ICP and cerebral blood flow (CBF). If these compensatory mechanismsare poor, even modest hypotension may induce a large transient increasein ICP and a significant transient reduction in CBF, with risks ofsecondary brain damage. 3) The ICPresponse to a bolus injection (PVI test) is sharply affected, viacerebral blood volume changes, by cerebral hemodynamics andautoregulation. We suggest that PVI tests may be used to extractinformation not only on intracranial compliance and CSF circulation,but also on the status of mechanisms controlling CBF. 相似文献
8.
Molecular phylogeny and divergence times of drosophilid species 总被引:32,自引:15,他引:17
The phylogenetic relationships and divergence times of 39 drosophilid
species were studied by using the coding region of the Adh gene. Four
genera--Scaptodrosophila, Zaprionus, Drosophila, and Scaptomyza (from
Hawaii)--and three Drosophila subgenera--Drosophila, Engiscaptomyza, and
Sophophora--were included. After conducting statistical analyses of the
nucleotide sequences of the Adh, Adhr (Adh-related gene), and nuclear rRNA
genes and a 905-bp segment of mitochondrial DNA, we used Scaptodrosophila
as the outgroup. The phylogenetic tree obtained showed that the first major
division of drosophilid species occurs between subgenus Sophophora (genus
Drosophila) and the group including subgenera Drosophila and Engiscaptomyza
plus the genera Zaprionus and Scaptomyza. Subgenus Sophophora is then
divided into D. willistoni and the clade of D. obscura and D. melanogaster
species groups. In the other major drosophilid group, Zaprionus first
separates from the other species, and then D. immigrans leaves the
remaining group of species. This remaining group then splits into the D.
repleta group and the Hawaiian drosophilid cluster (Hawaiian Drosophila,
Engiscaptomyza, and Scaptomyza). Engiscaptomyza and Scaptomyza are tightly
clustered. Each of the D. repleta, D. obscura, and D. melanogaster groups
is monophyletic. The splitting of subgenera Drosophila and Sophophora
apparently occurred about 40 Mya, whereas the D. repleta group and the
Hawaiian drosophilid cluster separated about 32 Mya. By contrast, the
splitting of Engiscaptomyza and Scaptomyza occurred only about 11 Mya,
suggesting that Scaptomyza experienced a rapid morphological evolution. The
D. obscura and D. melanogaster groups apparently diverged about 25 Mya.
Many of the D. repleta group species studied here have two functional Adh
genes (Adh-1 and Adh-2), and these duplicated genes can be explained by two
duplication events.
相似文献
9.
Cloning and characterization of the previously described Saccharomyces cerevisiae IMP1 gene, which was assumed to be a nuclear determinant involved in the nucleomitochondrial control of the utilization of galactose, demonstrate allelism to the GAL2 gene. Galactose metabolism does not necessarily involve the induction of the specific transport system coded by GAL2/IMP1, because a null mutant takes up galactose and grows on it. Data on galactose uptake are presented, and the dependence on ATP for constitutive and inducible galactose transport is discussed. These results can account for the inability of imp1/gal2 mutants to grow on galactose in a respiration-deficient background. Under these conditions, uptake was affected at the functional level but not at the biosynthetic level. 相似文献
10.
Sulfate reduction and S-oxidation in a moorland pool sediment 总被引:3,自引:2,他引:1
In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO4
2– reduction rates in the sediment, (2) depletion of SO4
2– in the overlying water column and (3) release of35S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO4
2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core35SO4
2– injection. Rates of SO4
2– consumption in the overlying water were estimated by changes in SO4
2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m–2 d–1. Rates of SO4
2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m–2 d–1 (November) to 0.43–1.81 mmol m–2 d–1 (July, August and April). Maximum rates of oxidation to SO4
2– in July 1990 estimated by combination of SO4
2– reduction rates and rates of in situ SO4
2– uptake in the enclosed water column were 10.3 and 10.5 mmol m–2 d–1 at an organic rich and at a sandy site respectively.Experiments with35S2– and35SO4
2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO4
2– and (2) the presence of mainly non SO4
2–-S derived from reduced S transported from the sediment into the overlying water. A35S2– tracer experiment showed that about 7% of35S2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author 相似文献