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151.

Background  

The Y-chromosomal diversity in the African buffalo (Syncerus caffer) population of Kruger National Park (KNP) is characterized by rainfall-driven haplotype frequency shifts between year cohorts. Stable Y-chromosomal polymorphism is difficult to reconcile with haplotype frequency variations without assuming frequency-dependent selection or specific interactions in the population dynamics of X- and Y-chromosomal genes, since otherwise the fittest haplotype would inevitably sweep to fixation. Stable Y-chromosomal polymorphism due one of these factors only seems possible when there are Y-chromosomal distorters of an equal sex ratio, which act by negatively affecting X-gametes, or Y-chromosomal suppressors of a female-biased sex ratio. These sex-ratio (SR) genes modify (suppress) gamete transmission in their own favour at a fitness cost, allowing for stable polymorphism.  相似文献   
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Precursor proteins from Neurospora crassa were correctly processed by a matrix extract from Vicia faba and cauliflower mitochondria. Processing yielded mature protein of the same molecular mass as mature Neurospora protein. The processing activity has two components. One is antigenically related to and of the same molecular mass as the processing enhancing protein of Neurospora. The second component was not recognized by antibody to the matrix processing protease from Neurospora mitochondria. The second component also houses the protease activity. Similar results were obtained using precursors to both the F1 beta subunit of the mitochondrial F0F1 ATPase and subunit V of the Rieske FeS complex from Neurospora. The beta subunit of the F0F1 ATPASE was processed to the mature form. Subunit V of the Rieske FeS complex was processed to the intermediate form only. Additional processing seen during import into plant mitochondria is not catalyzed by these proteins.  相似文献   
155.
Crystalline Bacillus subtilis alpha-amylase hydrolyses arnylopectin to a mixture Of D-gIUCOSe, maltose, and branched oligosaccharides (alpha-limit dextrins). The smallest such dextrin formed under the conditions of the experiment is a pentasaccharide. A combination of methylation analysis, periodate oxidation, and frag- mentation analysis with acid narrowed the pentasaccharide structure to two possibilities, but failed to distinguish between them. A rigid proof that the dextrin has the structure 6'-a-maltosylmaltotriose was obtained by application of enzymic degradation. Finally, the structure of the pentasaccharide was confirmed by enzymic synthesis. It is shown that the structural analysis of such oligosaccharides, derived from amylopectin, can be made by the use of enzymes alone, without resort to the more time-consuming, less-specific, and less-sensitive methods of chemical analysis. Conclusions are drawn regarding the action pattern of the B. subtilis arnylase.  相似文献   
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In this paper we elucidate part of the mechanism of the early stages of the biosynthesis of glycogen. This macromolecule is constructed by covalent apposition of glucose units to a protein, glycogenin, which remains covalently attached to the mature glycogen molecule. We have now isolated, in a 3500-fold purification, a protein from rabbit muscle that has the same Mr as glycogenin, is immunologically similar, and proves to be a self-glucosylating protein (SGP). When incubated with UDP-[14C]glucose, an average of one molecular proportion of glucose is incorporated into the protein, which we conclude is the same as glycogenin isolated from native glycogen. The native SGP appears to exist as a high-molecular-weight species that contains many identical subunits. Because the glucose that is self-incorporated can be released almost completely from the acceptor by glycogenolytic enzymes, the indication is that it was added to a preformed chain or chains of 1,4-linked alpha-glucose residues. This implies that SGP already carries an existing maltosaccharide chain or chains to which the glucose is added, rather than glucose being added directly to protein. The putative role of SGP in glycogen synthesis is confirmed by the fact that glucosylated SGP acts as a primer for glycogen synthase and branching enzyme to form high-molecular-weight material. SGP itself is completely free from glycogen synthase. The quantity of SGP in muscle is calculated to be about one-half the amount of glycogenin bound in glycogen.  相似文献   
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Viruses coopt cellular membrane transport to invade cells, establish intracellular sites of replication, and release progeny virions. Recent genome-wide RNA interference (RNAi) screens revealed that genetically divergent viruses require biosynthetic membrane transport by the COPI coatomer complex for efficient replication. Here we found that disrupting COPI function by RNAi inhibited an early stage of vesicular stomatitis virus (VSV) replication. To dissect which replication stage(s) was affected by coatomer inactivation, we used visual and biochemical assays to independently measure the efficiency of viral entry and gene expression in hamster (ldlF) cells depleted of the temperature-sensitive ε-COP subunit. We show that ε-COP depletion for 12 h caused a primary block to virus internalization and a secondary defect in viral gene expression. Using brefeldin A (BFA), a chemical inhibitor of COPI function, we demonstrate that short-term (1-h) BFA treatments inhibit VSV gene expression, while only long-term (12-h) treatments block virus entry. We conclude that prolonged coatomer inactivation perturbs cellular endocytic transport and thereby indirectly impairs VSV entry. Our results offer an explanation of why COPI coatomer is frequently identified in screens for cellular factors that support cell invasion by microbial pathogens.  相似文献   
160.
Members of the ATP-binding cassette (ABC) transporter family are essential proteins in species as diverse as archaea and humans. Their domain architecture has remained relatively fixed across these species, with rare exceptions. Here, we show one exception to be the trigalactosyldiacylglycerol 1, 2, and 3 (TGD1, -2, and -3) putative lipid transporter located at the chloroplast inner envelope membrane. TGD2 was previously shown to be in a complex of >500 kDa. We demonstrate that this complex also contains TGD1 and -3 and is very stable because it cannot be broken down by gentle denaturants to form a "core" complex similar in size to standard ABC transporters. The complex was purified from Pisum sativum (pea) chloroplast envelopes by native gel electrophoresis and examined by mass spectrometry. Identified proteins besides TGD1, -2, or -3 included a potassium efflux antiporter and a TIM17/22/23 family protein, but these were shown to be in separate high molecular mass complexes. Quantification of the complex components explained the size of the complex because 8-12 copies of the substrate-binding protein (TGD2) were found per functional transporter.  相似文献   
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