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941.
Genetic and morphological characterization of ftsB and nrdB mutants of Escherichia coli. 总被引:11,自引:8,他引:3
The ftsB gene of Escherichia coli is believed to be involved in cell division. In this report, we show that plasmids containing the nrdB gene could complement the ftsB mutation, suggesting that ftsB is an allele of nrdB. We compared changes in the cell shape of isogenic nrdA, nrdB, ftsB, and pbpB strains at permissive and restrictive temperatures. Although in rich medium all strains produced filaments at the restrictive temperature, in minimal medium only a 50 to 100% increase in mean cell mass occurred in the nrdA, nrdB, and ftsB strains. The typical pbpB cell division mutant also formed long filaments at low growth rates. Visualization of nucleoid structure by fluorescence microscopy demonstrated that nucleoid segregation was affected by nrdA, nrdB, and ftsB mutations at the restrictive temperature. Measurements of beta-galactosidase activity in lambda p(sfiA::lac) lysogenic nrdA, nrdB, and ftsB mutants in rich medium at the restrictive temperature showed that filamentation in the nrdA mutant was caused by sfiA (sulA) induction, while filamentation in nrdB and ftsB mutants was sfiA independent, suggesting an SOS-independent inhibition of cell division. 相似文献
942.
Ole Didrik Laerum Walter R. Paukovits 《Differentiation; research in biological diversity》1984,27(1-3):106-112
Abstract. Degeneration of the archenteron in middle gastrulae occurred in the presence of α,α'-dipyridyl or Zn2+ , inhibitors of prolyl hydroxylase. In the presence of these substances the archenteron degenerated and was eventually destroyed. Adding Fe2+ to the embryo culture containing α,α'-dipyridyl protected the archenteron from further degeneration, but the collapsed archenteron was not restored to the upright position. At the late gastrula stage, α,α'-dipyridyl did not cause the degeneration of the archenteron. Treatment of the embryos by α,α'-dipyridyl, starting at the swimming blastula stage, resulted in the production of many mesenchyme-like cells but archenteron was not produced in the embryos. Addition of Fe2+ to α,α'-dipyridyl culture, just before the beginning of gastrulation of normal embryos, resulted in the formation of normal archenteron. α,α'-Dipyridyl inhibited hydroxylation of proline residues of collagen in sea urchin embryos and Fe2+ prevented the inhibition by α,α'-dipyridyl. Respiration was not inhibited by α,α'-dipyridyl. 相似文献
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944.
Biogeographical analyses are applied to skipper (Hesperioidea) presence/absence data from the Western Mediterranean mainland
and the three largest islands (Sardinia, Corsica and Sicily) in order to identify potential conservation issues. The analyses
performed on species, both collectively and individually, indicate that regional species richness and occurrence in the Mediterranean
zone are largely predicted by latitude and area but that islands have impoverished faunas. Several species, predicted to be
present on these islands from logistic regression of their continental distributions, are actually absent. The number of species
predicted to be present from logistic regression analyses for each island, closely matched the number of species predicted
to occur in regional-focused multiple regression analysis. This suggests that missing species have been identified. When compared
with species that occur in Sicily and Corsica, the missing species are shown to differ for ecological traits, mainly those
linked to altitudinal tolerance. No ecological distinctions were disclosed for Sardinian skippers suggesting a mainly stochastic
colonisation. These results, and those from an analogous study carried out on Papilionoidea, point to Hesperioidea having
(i) overall more impoverished faunas on islands and (ii) being subject to stochastic or historical colonisation events more
than Papilionoidea. Species not predicted to occur on islands based on their mainland distributions and ecological traits,
are foci for conservation attention. However, as many species becoming extinct on the islands may be irreplaceable, all species,
in particular the Sardinian ones, deserve to be conserved. 相似文献
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The forty-two days long experiment was conducted on a total of 1000 Arbor Acres broilers, divided into two groups. Both groups
of broilers were fed with a commercial feed mixture which consisted of standard feedstuffs and contained enough nutrients
regarding the requirements. During the first three weeks of the trial, corn naturally contaminated with AFB1 0.0445 ppm per kg dry matter was used in the amount of 20% in the experimental group, while AFB1 free corn was given to birds in the control group. After the period of toxin administration until the end of the trial, broilers
from both groups were normally fed another 5 weeks with uncontaminated feed.
In the first phase of the trial, broilers in the control groups had an average daily gain (ADG) of 31 g, average daily feed
intake (ADFI) of 45 g and a feed: gain ratio (FCR) of 1.42. In the same time, experimental broilers achieved an ADG of 25
g, ADFI of 35 g and a FCR of 1.39. During the whole period of the trial, control and experimental broilers achieved 49.12
g, 95.24 g and 1.94 and 39.71 g, 86.90 g and 2.19, respectively. 相似文献