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71.
Synonymous substitution rates in mitochondrial and nuclear genes of Drosophila were compared. To make accurate comparisons, we considered the following: (1) relative synonymous rates, which do not require
divergence time estimates, should be used; (2) methods estimating divergence should take into account base composition; (3)
only very closely related species should be used to avoid effects of saturation; (4) the heterogeneity of rates should be
examined. We modified the methods estimating synonymous substitution numbers to account for base composition bias. By using
these methods, we found that mitochondrial genes have 1.7–3.4 times higher synonymous substitution rates than the fastest
nuclear genes or 4.5–9.0 times higher rates than the average nuclear genes. The average rate of synonymous transversions was
2.7 (estimated from the melanogaster species subgroup) or 2.9 (estimated from the obscura group) times higher in mitochondrial genes than in nuclear genes. Synonymous transversions in mitochondrial genes occurred
at an approximately equivalent rate to those in the fastest nuclear genes. This last result is not consistent with the hypothesis
that the difference in turnover rates between mitochondrial and nuclear genomes is the major factor determining higher synonymous
substitution rates in mtDNA. We conclude that the difference in synonymous substitution rates is due to a combination of two
factors: a higher transitional mutation rate in mtDNA and constraints on nuclear genes due to selection for codon usage.
Received: 27 November 1996 / Accepted: 8 May 1997 相似文献
72.
Systematic studies were undertaken on the Caloglossa continua ( Okamura) King et Puttock complex from Japan, Singapore, and Australia, based on morphology and reproductive compatibility. Specimens from Japan had two to six cell rows derived from a nodal axial cell, at the margin opposite the branch, whereas those from Australia possessed only a single cell row. Specimens from Singapore formed one to four cell rows per nodal axial cell and always contained at least one single cell row on any one thallus. These differences were maintained in cultured materials over a range of temperatures or salinities. Type material of C. continua had the same morphology as the Japanese specimens in this study. Carpospores discharged from the Japanese isolate germinated at 10°C, whereas those from Singapore and Australia died at this temperature. In hybridization experiments, the Japanese entity was completely nonfertile with both the Singaporean and Australian isolates. Many pseudocystocarps were produced in the crossing between the male from Australia and the female from Singapore, although the reciprocal combination did not produce any such structures. On the basis of the discontinuous morphology coupled with the complete reproductive isolation, the entities from Singapore and Australia are described here as C. monosticha sp. nov. The entities with multiple cell rows likely expanded their geographic range from tropical regions, where the majority of Caloglossa species are now distributed, to high-latitude regions, and such an expansion would be associated with acquiring low-temperature tolerance . 相似文献
73.
The effect of season and group size on survivorship and larval growth in Plagiodera versicolora 总被引:1,自引:0,他引:1
MARY L. CROWE 《Ecological Entomology》1995,20(1):27-32
Abstract.
- 1 The larvae of the multivoltine imported willow leaf beetle, Plagiodera versicolora (Laicharting), are found in larval aggregations during the first half of the larval stage. An experimental study was conducted to test for seasonal (brood) and group size effects on larval fitness. For each of the three broods, egg group sizes of 1, 4, 8, 16 , 24 and 32 were established in the field and monitored for the first 6 days post-hatching.
- 2 There was no effect of group size on larval weight, but there was a significant effect of group size on survival. Individuals from group size 16 had the highest survival, which coincides with the mean natural cluster size of 15.3 eggs.
- 3 There were no significant interactions between brood and group size.
- 4 The effect of larval weight on adult fitness was determined in the laboratory and the field. Larval weight was correlated with egg production in the laboratory but not in the field.
74.
75.
Human erythrocytes were treated by a series of SH-reagents, including maleimides, iodo compounds, mercurials and oxidizing agents. Rates of Li efflux into Na-rich medium, Li leak and Lii-Nao countertransport were then determined. Of the 13 different reagents studied, only N-ethylmaleimide, iodoacetamide and iodoacetate inhibited selectively the countertransport activity. The effect of the various reagents indicates that the sensitive SH-groups of the countertransport system are not externally exposed. N-Ethylmaleimide was used to probe for changes elicited by substrate cations in Lii-Nao countertransport. In Na- and Li-free medium, inhibition of Lii-Nao countertransport by N-ethylmaleimide of 35% was reached within 2 s. In Na or Li medium, maximal inhibition was twice as great, but was attained much more slowly, within 10 min. Kinetic data and Hill plot analysis indicate the involvement of two classes of SH-groups: one expressed in the various media with and without substrate cations, and an additional one, which becomes specifically available to N-ethylmaleimide in the presence of external Na or Li. The affinity of Na to the site promoting inhibition by N-ethylmaleimide (apparent Km 12 mM) is higher than the affinity of Na to its external countertransport site (apparent Km 25 mM), as reported by Sarakadi, B., Alifimoff, J.K., Gunn, R.B. and Tosteson, D.C. (1978) J. Gen. Physiol. 72, 249–265). Reactivity of was not modified by the media tested. It is concluded that external Na and Li cause a conformational change in the protein(s) of the countertransport system in human erythrocytes. 相似文献
76.
C. Benito A. M. Figueiras M. T. Gonzalez-Jaen 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1984,68(6):555-557
Summary Structural genes for the isozymes of phosphogluco mutase (PGM) (EC 2.7.5.1) have been located on chromosome arms 4A, 4BL and 4DS of hexaploid wheat. These results support the homoeologies observed among these chromosome arms and also support the notion of conservation of gene synteny groups within the Triticinae. 相似文献
77.
鄂东南早白垩世灵乡群孢粉组合 总被引:1,自引:0,他引:1
张振来 《Acta Botanica Sinica》1984,(6)
本文根据从大冶灵乡-陈重山剖面的中部、灵乡狮子山东侧采坑和鄂城太和1孔的相当层位中所获得的孢粉组合(共67属120余种,其中新种9个,新联合2个),认为灵乡群孢粉组合属于 Classopollis、Psophosphaera-Cicatricosisporites、Schizaeoisporites-没有或极个别的出现被子植物花粉的组合类型,其地质时代应为早白垩世早期-中期(凡兰吟期-巴列姆期)。并推测鄂东南地区当时的气候属于偏干旱的热带-亚热带型。 相似文献
78.
Mikael Esmann 《生物化学与生物物理学报:生物膜》1982,688(1):260-270
1. Modification of the Class II sulphydryl groups on the (Na+ + K+)-ATPase from rectal glands of Squalus acanthias with N-ethylmaleimide has been used to detect conformational changes in the protein. The rates of inactivation of the enzyme and the incorporation of N-ethylmaleimide depend on the ligands present in the incubation medium. With 150 mM K+ the rate of inactivation is largest (k1 = 1.73 mM?1 · min?1) and four SH groups per α-subunit are modified. The rate of inactivation in the presence of 150 mM Na+ is smaller (k1 = 1.08 mM?1 · min-1) but the incorporation of N-ethylmaleimide is the same as with K+. 2. ATP in micromolar concentrations protects the Class II groups in the presence of Na+ (k1 = 0.08 mM?1 · min?1 at saturating ATP) and the incorporation id drastically reduced. ATP in millimolar concentrations protects the Class II groups partially in the presence of K+ (k1 = 1.08 mM?1 · min?1) and three SH groups are labelled per α subunit. 3. The K+ -dependent phosphatase is inhibited in parallel to the (Na+ + K+)-ATPase under all conditions, and the ligand-dependent incorporation of N-ethylmaleimide was on the α-subunit only. 4. It is shown that the difference between the Na+ and K+ conformations sensed with N-ethylmaleimide depends on the pH of the incubation medium. At pH 6 there is a very small difference between the rates of inactivation in the presence of Na+ and K+, but at higher pH the difference increases. It is also shown that the rate of inactivation has a minimum at pH 6.9, which suggests that the conformation of the enzyme changes with pH. 5. Modification of the Class III groups with N-ethylmaleimide-whereby the enzyme activity is reduced from about 16% to zero-shows that these groups are also sensitive to conformational changes. As with the Class II groups, ATP in micromolar concentrations protects in the presence of Na+ relative to Na+ or K+ alone. ATP in millimolar concentrations with K+ present increases the rate of inactivation relative to K+ alone, in contrast to the effect on the Class II groups. 6. Modification of the Class II groups with a maleimide spin label shows a difference between Class II groups labelled in the presence of Na+ (or K+) and Class II groups labelled in the presence of K + ATP, in agreement with the difference in incorporation of N-ethylmaleimide. The spectra suggest that the SH group protected by ATP in the presence of K+ is buried in the protein. 7. The results suggest that at least four different conformations of the (Na+ + K+)-ATPase can be sensed with N-ethylmaleimide: (i) a Na+ form of the enzyme with ATP bound to a high-affinity site (E1-Na-ATP); (ii) a Na+ form without ATP bound (E1-Na); (iii) a K+ form without ATP bound (E2-K); and (iv) an enzyme form with ATP bound to a low-affinity site in the presence of K+, probably and E1-K-ATP form. 相似文献
79.
Pretreatment of Chang liver cells with (0.5 or 1 mM) stimulated Na+-independent uptake of leucine at low concentrations (?1 mM). The stimulatory effect of on the uptake of leucine measured in Na+-replete medium was completely blocked by the addition of (5 mM), which shows that the L system participates in the stimulation. The Na+-dependent uptake of glycine was depressed by pretreatment. The stimulation of the Na+-independent component of leucine uptake continued for at least 30 min after treatment, while the inhibition of glycine uptake was progressive with time and the Na+-dependent uptake of leucine became depressed later, after the treatment. It has been demonstrated that treatment of cells with is capable of increasing the Na+-independent influx of leucine and at the same time slightly decreasing the efflux of it. These results suggest that attacks the Na+-independent system of amino acid transport at the reactive SH groups(s) of relevant protein(s) in favor of specific activation of that system in this cell. 相似文献
80.
四种中草药对大鼠半乳糖性白内障氧化还原物质及糖类含量的影响 总被引:1,自引:0,他引:1
对正常和半乳糖性白内障及给中草药的大鼠晶状体中某些吡啶核苷酸成分、糖类、非蛋白质巯基的含量进行了比较。结果表明,在白内障晶状体中,NADPH及非蛋白质巯基的含量明显低于正常晶状体的,而NADP、半乳糖及半乳糖醇的含量明显高于正常晶状体的;当注射半乳糖的同时分别用黄岑、石斛、菟丝子及玉蝴蝶四种中草药水煎剂灌胃,上述变化为基本恢复至正常晶状体的水平。表明四种中草药对晶状体中的异常生化变化具有阻止及纠正作用。 相似文献