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991.
The evolutionary stability of haploid–diploid life cycles is still controversial. Mathematical models indicate that niche differences between ploidy phases may be a necessary condition for the evolution and maintenance of these life cycles. Nevertheless, experimental support for this prediction remains elusive. In the present work, we explored this hypothesis in natural populations of the brown alga Ectocarpus. Consistent with the life cycle described in culture, Ectocarpus crouaniorum in NW France and E. siliculosus in SW Italy exhibited an alternation between haploid gametophytes and diploid sporophytes. Our field data invalidated, however, the long‐standing view of an isomorphic alternation of generations. Gametophytes and sporophytes displayed marked differences in size and, conforming to theoretical predictions, occupied different spatiotemporal niches. Gametophytes were found almost exclusively on the alga Scytosiphon lomentaria during spring whereas sporophytes were present year‐round on abiotic substrata. Paradoxically, E. siliculosus in NW France exhibited similar habitat usage despite the absence of alternation of ploidy phases. Diploid sporophytes grew both epilithically and epiphytically, and this mainly asexual population gained the same ecological advantage postulated for haploid–diploid populations. Consequently, an ecological interpretation of the niche differences between haploid and diploid individuals does not seem to satisfactorily explain the evolution of the Ectocarpus life cycle.  相似文献   
992.
Achromobacter denitrificans YD35 is an NO2-tolerant bacterium that expresses the aconitase genes acnA3, acnA4, and acnB, of which acnA3 is essential for growth tolerance against 100 mm NO2. Atmospheric oxygen inactivated AcnA3 at a rate of 1.6 × 10−3 min−1, which was 2.7- and 37-fold lower compared with AcnA4 and AcnB, respectively. Stoichiometric titration showed that the [4Fe-4S]2+ cluster of AcnA3 was more stable against oxidative inactivation by ferricyanide than that of AcnA4. Aconitase activity of AcnA3 persisted against high NO2 levels that generate reactive nitrogen species with an inactivation rate constant of k = 7.8 × 10−3 min−1, which was 1.6- and 7.8-fold lower than those for AcnA4 and AcnB, respectively. When exposed to NO2, the acnA3 mutant (AcnA3Tn) accumulated higher levels of cellular citrate compared with the other aconitase mutants, indicating that AcnA3 is a major producer of cellular aconitase activity. The extreme resistance of AcnA3 against oxidation and reactive nitrogen species apparently contributes to bacterial NO2 tolerance. AcnA3Tn accumulated less cellular NADH and ATP compared with YD35 under our culture conditions. The accumulation of more NO by AcnA3Tn suggested that NADH-dependent enzymes detoxify NO for survival in a high NO2 milieu. This novel aconitase is distributed in Alcaligenaceae bacteria, including pathogens and denitrifiers, and it appears to contribute to a novel NO2 tolerance mechanism in this strain.  相似文献   
993.
Photoautotrophic bacteria have developed mechanisms to maintain K+ homeostasis under conditions of changing ionic concentrations in the environment. Synechocystis sp. strain PCC 6803 contains genes encoding a well-characterized Ktr-type K+ uptake transporter (Ktr) and a putative ATP-dependent transporter specific for K+ (Kdp). The contributions of each of these K+ transport systems to cellular K+ homeostasis have not yet been defined conclusively. To verify the functionality of Kdp, kdp genes were expressed in Escherichia coli, where Kdp conferred K+ uptake, albeit with lower rates than were conferred by Ktr. An on-chip microfluidic device enabled monitoring of the biphasic initial volume recovery of single Synechocystis cells after hyperosmotic shock. Here, Ktr functioned as the primary K+ uptake system during the first recovery phase, whereas Kdp did not contribute significantly. The expression of the kdp operon in Synechocystis was induced by extracellular K+ depletion. Correspondingly, Kdp-mediated K+ uptake supported Synechocystis cell growth with trace amounts of external potassium. This induction of kdp expression depended on two adjacent genes, hik20 and rre19, encoding a putative two-component system. The circadian expression of kdp and ktr peaked at subjective dawn, which may support the acquisition of K+ required for the regular diurnal photosynthetic metabolism. These results indicate that Kdp contributes to the maintenance of a basal intracellular K+ concentration under conditions of limited K+ in natural environments, whereas Ktr mediates fast potassium movements in the presence of greater K+ availability. Through their distinct activities, both Ktr and Kdp coordinate the responses of Synechocystis to changes in K+ levels under fluctuating environmental conditions.  相似文献   
994.
In addition to its role in DNA repair, nuclear poly(ADP-ribose) polymerase-1 (PARP-1) mediates brain damage when it is over-activated by oxidative/nitrosative stress. Nonetheless, it remains unclear how PARP-1 is activated in neuropathological contexts. Here we report that PARP-1 interacts with a pool of glyceradehyde-3-phosphate dehydrogenase (GAPDH) that translocates into the nucleus under oxidative/nitrosative stress both in vitro and in vivo. A well conserved amino acid at the N terminus of GAPDH determines its protein binding with PARP-1. Wild-type (WT) but not mutant GAPDH, that lacks the ability to bind PARP-1, can promote PARP-1 activation. Importantly, disrupting this interaction significantly diminishes PARP-1 overactivation and protects against both brain damage and neurological deficits induced by middle cerebral artery occlusion/reperfusion in a rat stroke model. Together, these findings suggest that nuclear GAPDH is a key regulator of PARP-1 activity, and its signaling underlies the pathology of oxidative/nitrosative stress-induced brain damage including stroke.  相似文献   
995.
996.
997.
Scytosiphon lomentaria (Scytosiphonaceae, Ectocarpales) is believed to include some cryptic species, particularly in the Pacific. We attempted to delimit these species in Japan using mitochondrial cox1 and cox3 and nuclear ITS2 and the second intron of the centrin gene (cetn‐int2). Fifty‐three cox1+cox3 mitotypes, 26 ITS2 ribotypes and 45 cetn‐int2 haplotypes were found in 107 samples collected from 33 localities in Japan. Based on phylogenetic analyses, similar sequence types were grouped into ten mitogroups, eight ribogroups and six cetn‐int2 haplogroups (sequence‐type groups). From the molecular trees and combinations of the mito‐, ribo‐ and haplogroups, three cryptic species were apparent (Groups I–III). Group I, widely distributed on Pacific coasts, was highly supported by all molecular trees, whereas Groups II (North Pacific) and III (Northwestern Pacific and Australasia) were more closely related to each other. However, sequence‐type‐group combinations that would be characteristic of hybrids between Groups II and III were not detected, suggesting no gene flow between the two Groups. Further investigations of an additional 127 sympatrically growing plants supported the absence of gene flow between Groups II and III. Four samples did not belong to any of the Groups I–III and possibly represent additional species.  相似文献   
998.
Adults of the three papilionid butterflies, Papilio helenus L., Papilio machaon L. and Papilio memnon L., exhibit seasonal diphenism comprising spring and summer morphs. To elucidate the physiological mechanism underlying seasonal morph development in papilionid butterflies, we investigated whether a cerebral factor showing summer‐morph‐producing hormone (SMPH) activity is present in the brain of three Papilio species using an assay system with chilled male short‐day pupae of P. xuthus L. When 2% NaCl extracts derived from 20 larval brains of the three species were injected into abdomens of chilled male short‐day pupae of P. xuthus, all recipients destined to develop into spring‐morph adults developed into summer‐ and intermediate‐morph adults. On the other hand, all recipients injected with distilled water as a control developed into spring‐morph adults. These results indicate that a cerebral factor showing SMPH activity is present in the larval brain of the three Papilio species. Additionally, all recipients injected with 2% NaCl extracts derived from 20 adult brains of Bombyx mori L. also developed into summer‐ and intermediate‐morph adults. The results revealed that SMPH or a cerebral factor showing SMPH activity is widely distributed among lepidopteran insects.  相似文献   
999.
Tryptophan (Trp) residues are frequently found in the hydrophobic cores of proteins, and therefore, their side-chain conformations, especially the precise locations of the bulky indole rings, are critical for determining structures by NMR. However, when analyzing [U–13C,15N]-proteins, the observation and assignment of the ring signals are often hampered by excessive overlaps and tight spin couplings. These difficulties have been greatly alleviated by using stereo-array isotope labeled (SAIL) proteins, which are composed of isotope-labeled amino acids optimized for unambiguous side-chain NMR assignment, exclusively through the 13C–13C and 13C–1H spin coupling networks (Kainosho et al. in Nature 440:52–57, 2006). In this paper, we propose an alternative type of SAIL-Trp with the [ζ2,ζ3-2H2; δ1,ε3,η2-13C3; ε1-15N]-indole ring ([12Cγ, 12Cε2] SAIL-Trp), which provides a more robust way to correlate the 1Hβ, 1Hα, and 1HN to the 1Hδ1 and 1Hε3 through the intra-residue NOEs. The assignment of the 1Hδ1/13Cδ1 and 1Hε3/13Cε3 signals can thus be transferred to the 1Hε1/15Nε1 and 1Hη2/13Cη2 signals, as with the previous type of SAIL-Trp, which has an extra 13C at the Cγ of the ring. By taking advantage of the stereospecific deuteration of one of the prochiral β-methylene protons, which was 1Hβ2 in this experiment, one can determine the side-chain conformation of the Trp residue including the χ2 angle, which is especially important for Trp residues, as they can adopt three preferred conformations. We demonstrated the usefulness of [12Cγ,12Cε2] SAIL-Trp for the 12 kDa DNA binding domain of mouse c-Myb protein (Myb-R2R3), which contains six Trp residues.  相似文献   
1000.
Danforth'sshort-tail (Sd) mouse is a semi-dominant mutation affecting the development of the vertebral column. Although the notochord degenerates completely by embryonic day 9.5, the vertebral column exists up to the lumber region, suggesting that the floor plate can substitute for notochord function. We previously established the mutant mouse line, Skt(Gt), through gene trap mutagenesis and identified the novel gene, Skt, which was mapped 0.95cM distal to the Sd locus. Taking advantage of the fact that monitoring notochordal development and genotyping of the Sd locus can be performed using the Skt(Gt) allele, we assessed the development of the vertebra, notochord, somite, floor plate and sclerotome in +-+/+-Skt(Gt), Sd-+/+-+, Sd-Skt(Gt)/+-+, Sd-Skt(Gt)/+-Skt(Gt), Sd-+/Sd-+ and Sd-Skt(Gt)/Sd-Skt(Gt) embryos. In Sd homozygous mutants with a C57BL/6 genetic background, the vertebral column was truncated in the 6th thoracic vertebra, which was more severe than previously reported. The floor plate and sclerotome developed to the level of somite before notochord degeneration and the number of remaining vertebrae corresponded well with the level of development of the floor plate and sclerotome. Defects to the sclerotome and subsequent vertebral development were not due to failure of somitogenesis. Taken together, these results suggest that the notochord induced floor plate development before degeneration, and that the remaining floor plate is sufficient for maintenance of differentiation of the somite into the sclerotome and vertebra in the absence of the notochord.  相似文献   
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