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1.
Common regulatory elements control symbiotic and microaerobic induction of nifA in Rhizobium meliloti. 总被引:24,自引:2,他引:22
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E L Virts S W Stanfield D R Helinski G S Ditta 《Proceedings of the National Academy of Sciences of the United States of America》1988,85(9):3062-3065
We have previously demonstrated that the nifA promoter (nifAp) of Rhizobium meliloti is inducible under microaerobic conditions in the absence of alfalfa. Here we show that microaerobic activation of nifAp involves both cis- and trans-acting regulatory controls identical to those used symbiotically. The start site for nifA mRNA synthesis was found to be the same during symbiosis and microaerobiosis, and a deletion analysis of nifAp demonstrated that DNA between positions -62 and -45 is essential for induction. Mutants isolated as being unable to induce nifA microaerobically also were found to be defective in symbiotic nitrogen fixation with alfalfa. Such mutants form nodules that are equivalent cytologically to those induced by nifA::Tn5 mutants. Genetic and structural studies have localized the mutations to a cluster of fix genes 200 kilobases distant from the nod-nif region on the pSym megaplasmid [Renalier, M.-H., Batut, J., Ghai, J., Terzaghi, B., Gherardi, M., David, M., Garnerone, A.-M., Vasse, J., Truchet, G., Huguet, T. & Boistard, P. (1987) J. Bacteriol. 169, 2231-2238]. 相似文献
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The mammalian neocortex is functionally organized into numerous specialized "areas." The distinct functional properties characteristic of each area are in large part due to connectional and architectural differences among the areas. However, these "area-specific" features which distinguish mature areas are not apparent early in the development of neocortex. We have used heterotopic cortical transplantation to examine whether these area-specific features are prespecified or emerge as a result of epigenetic interactions. Here, we review our studies in which late fetal rat cortex was transplanted heterotopically into the cortex of newborn rats to test its capacity to differentiate features normally unique to other cortical areas. We find that regions of the developing neocortex have similar potentials to differentiate the connectivity and functional architecture that distinguish neocortical areas in the adult. We conclude that the neocortical neuroepithelium generates comparable populations of cells across its extent, and when exposed to the same extrinsic cues, these populations can differentiate in comparable ways. These studies support the concept that the neocortical neuroepithelium generates a "protocortex" (20), specified to have fundamental cortical features but lacking a rigid specification of "area-specific" features. 相似文献
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Actions of some anions on electrical properties and mechanical threshold of frog twitch muscle 总被引:9,自引:1,他引:9
1. Using two micro-electrodes in a point-voltage clamp technique, the effects of the lyotropic anions, NO(3) (-), Br(-), I(-), SCN(-), and CH(3)SO(4) (-), and of SO(4) (2-) on the mechanical threshold and electrical properties of frog sartorius muscle were studied.2. In chloride Ringer solution the spike threshold was -59 mV, mechanical threshold -48 mV, and the threshold for delayed rectification of the total current at about 100 msec -52 mV.3. When Cl(-) was replaced by one of the lyotropic anions, the effective resistance determined at -100 mV tended to increase. But, because of the variability of the effective resistance in individual fibres, most lyotropic anions did not cause a statistically significant increase in the effective resistance. Only I(-) and SO(4) (2-) significantly increased the effective resistance.4. Most lyotropic anions had no significant effect on the spike threshold; I(-), at 58 mM, lowered it slightly. Sulphate raised the threshold.5. Tetrodotoxin (0.1 mug/ml.) abolished the spikes, but did not affect the mechanical and delayed rectification thresholds. It was, therefore, used to pre-treat all preparations for determining these thresholds.6. All lyotropic anions lowered the mechanical and the delayed rectification thresholds, the order of effectiveness being approximately SCN(-) > I(-) > NO(3) (-) > CH(3)SO(4) (-) > Br(-). As in Cl(-) Ringer, the two thresholds lay very close together in every case. Sulphate raised slightly both the mechanical and delayed rectification thresholds, again in close parallel.7. This close agreement of the mechanical and delayed rectification thresholds is not caused by movement artifact, because in fibres in which visible contractions were eliminated with hypertonic solutions the delayed rectification thresholds were the same as those in contracting fibres.8. In spite of the close agreement, reasons are given to doubt a direct causal relationship between the mechanical and delayed rectification thresholds.9. Nitrate apparently had little effect on the rate of inactivation of the outward current, or on the relation between steady-state inactivation and membrane potential. 相似文献
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Bals-Pratsch M; De Geyter C; Muller T; Frieling U; Lerchl A; Pirke KM; Hanker JP; Becker-Carus C; Nieschlag E 《Human reproduction (Oxford, England)》1997,12(5):896-904
Preliminary data have suggested that female infertility due to corpus
luteum insufficiency may be caused by subclinical hypothyroidism
[exaggerated thyroid-stimulating hormone (TSH) response to thyrotrophin-
releasing hormone (TRH) stimulation]. L-Thyroxine supplementation has been
recommended to achieve pregnancies in subclinical hypothyroid women. This
controlled study was carried out in order to investigate the biochemical
diagnosis of subclinical hypothyroidism as a possible infertility factor.
Five infertile patients (aged 25-36 years) with subclinical hypothyroidism
(n = 4, stimulated TSH >20 microU/ml) or primary hypothyroidism (n = 1)
and five healthy controls (aged 22-39 years) with normal thyroid function
(stimulated TSH <15 microU/ml), regular cycles and no history of
infertility were studied in the early follicular phase. In the pre-study
evaluation, eight of 23 volunteers (34.8%) had to be excluded because of
subclinical hypothyroidism with stimulated TSH values (TSHs) >15
microU/ml. Cycle function of patients and controls was compared by the
method of LH pulse pattern analysis. Therefore blood samples were drawn
every 10 min during a 24 h period. Sleep was recorded from midnight to 7
a.m. Repetition of the TRH tests at the end of the 24 h blood sampling
period confirmed the difference in stimulated TSH values of the two study
groups. Pulse analysis for luteinizing hormone (LH), TSH and prolactin
showed no differences between patients and controls for pulse frequency,
amplitude, height, length, area under curve (AUC) and the 24 h mean. Even
the hypothyroid patient had a normal LH pulse pattern. Additional
measurement of melatonin in pooled sera every 30 min gave the
well-documented diurnal profiles during day and night for both groups.
Patients had significantly higher melatonin values at seven time points
during the night. Peaks for LH, TSH, prolactin and cortisol were correlated
with the sleep stages wake, rapid eye movement, 1 + 2 and 3 + 4. We
concluded that corpus luteum insufficiency in female infertility cannot be
explained by subclinical hypothyroidism and thus should not be treated with
L-thyroxine for fertility reasons.
相似文献