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361.
Lewisia kelloggii has been understood as a rare plant with a disjunct range in California and Idaho. Examination of herbarium specimens and analysis of isozymes in 6 Idaho and 7 California populations revealed consistent differences between plants of the 2 states. Fixed differences in alleles at 2 loci (AAT2 and PGI1) distinguished Idaho from California plants. Genetic identities based on isozymes between Idaho and California populations averaged 0.58, lower than the average for congeneric plant species. Idaho plants were smaller than most California plants, but California plants were variable. The most consistent morphological difference between Idaho and California specimens was the difference in the number of glands on the margins of bracts and sepals. Idaho plants had 0 (-5) pink glands on each margin of these organs, all on teeth near the tips. In California plants these organs had 12-25 glands on each margin, the distal ones elevated on teeth and the proximal ones sessile. We recognize the Idaho plants as a new species, L. sacajaweana , and retain the name L. kelloggii for the California populations. 相似文献
362.
Lekelia D. Jenkins 《Studies in history and philosophy of science》2010,41(1):75-85
This paper explores the evolution of a trading zone by organizing the case study of turtle excluder devices within the model proposed by Collins et al. (2007). The case study offers evidence that trading zones do evolve and that the concepts of enforced and fractionated trading zones hold practical utility for describing and defining the complexities of actual exchanges. In this case a trading zone evolved from enforced to fractionated and ultimately diverged into two trading zones. For each step of the evolution I describe the forces that drove these transitions. Finally, I present an adapted trading zone model that is conceptually a better fit for the turtle excluder device case study. 相似文献
363.
364.
Carl D. Marti 《西北部美国博物学家》2011,46(2)
An investigation of the diet of the Common Barn-owl ( Tyto alba ) on Antelope Island, Great Salt Lake, Utah, yielded four mammal species not previously known to occur on any island in the Great Salt Lake ( Microtus pennsylvanicus, M. montanus, Ondatra zibethicus , and a Sorex sp.). Two other species, known from other islands, were added to the list of fauna of Antelope Island ( Perognathus parvus and Reithrodontomys megalotis ). The barn owl diet on Antelope Island was remarkably like that of barn owls feeding in farmlands adjacent to the Great Salt Lake despite major vegetational differences. 相似文献
365.
366.
367.
Christian Dölle Marc Niere Emilia Lohndal Mathias Ziegler 《Cellular and molecular life sciences : CMLS》2010,67(3):433-443
Poly-ADP-ribose polymerases (PARPs) use NAD+ as substrate to generate polymers of ADP-ribose. We targeted the catalytic domain of human PARP1 as molecular NAD+ detector into cellular organelles. Immunochemical detection of polymers demonstrated distinct subcellular NAD+ pools in mitochondria, peroxisomes and, surprisingly, in the endoplasmic reticulum and the Golgi complex. Polymers did not
accumulate within the mitochondrial intermembrane space or the cytosol. We demonstrate the suitability of this compartment-specific
NAD+ and poly-ADP-ribose turnover to establish intra-organellar protein localization. For overexpressed proteins, genetically
endowed with PARP activity, detection of polymers indicates segregation from the cytosol and consequently intra-organellar
residence. In mitochondria, polymer build-up reveals matrix localization of the PARP fusion protein. Compared to presently
used fusion tags for subcellular protein localization, these are substantial improvements in resolution. We thus established
a novel molecular tool applicable for studies of subcellular NAD metabolism and protein localization. 相似文献
368.
Self peptides bound to self major histocompatibility complex (MHC) molecules have been implicated both in positive and in negative selection of T cells during intrathymic development. We report here that the novel MHC-restricted monoclonal antibody Y-Ae detects the MHC class II bound form of a major self peptide. Y-Ae binds approximately 12% of the relevant MHC class II molecules on self antigen presenting cells. The peptide detected by Y-Ae is one of several major peptides eluted from the MHC molecule. These data suggest that self peptides presented by self MHC class II molecules at densities sufficient to signal a CD4 T cell are of very limited complexity. Furthermore, as Y-Ae stains antigen presenting cells that mediate negative selection but not thymic cortical epithelial cells that drive positive selection, differential expression of self peptide:self MHC class II complexes may be a key feature of intrathymic selection. 相似文献
369.
R E Hill J Favor B L Hogan C C Ton G F Saunders I M Hanson J Prosser T Jordan N D Hastie V van Heyningen 《Nature》1991,354(6354):522-525
370.
The L-type voltage-dependent calcium channel is an important link in excitation-contraction coupling of muscle cells (reviewed in refs 2 and 3). The channel has two functional characteristics: calcium permeation and receptor sites for calcium antagonists. In skeletal muscle the channel is a complex of five subunits, alpha 1, alpha 2, beta, gamma and delta. Complementary DNAs to these subunits have been cloned and their amino-acid sequences deduced. The skeletal muscle alpha 1 subunit cDNA expressed in L cells manifests as specific calcium-ion permeation, as well as sensitivity to the three classes of organic calcium-channel blockers. We report here that coexpression of the alpha 1 subunit with other subunits results in significant changes in dihydropyridine binding and gating properties. The available number of drug receptor sites increases 10-fold with an alpha 1 beta combination, whereas the affinity of the dihydropyridine binding site remains unchanged. Also, the presence of the beta subunit accelerates activation and inactivation kinetics of the calcium-channel current. 相似文献