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The availability of tyrosyl residues to surface iodination was analyzed for histone 2A (H2A), histone 2B (H2B), and the H2A/H2B complex. When H2A is free in solution (200 mM NaCl, pH 7.4) tyrosine-39 and one or both tyrosines-50 and -57 were readily iodinated. Tyrosines-83 and -121 of H2B were iodinated, both when the histone was free in solution and when it was associated with H2A, while tyrosines-37, -40, and -42 of H2B were not iodinated under either condition. When H2A and H2B were associated or covalently cross-linked, all tyrosyl residues of H2A were unavailable for iodination. We also found that the iodination of nondenatured H2A and H2B did not inhibit formation of the H2A/H2B complex. These results indicate that the amino-terminal regions of the hydrophobic portions of H2A and H2B undergo significant conformational changes upon formation of the H2A/H2B complex. These conformational shifts occur in the same region of the H2A/H2B complex that contains a contact site between H2A and H2B in the nucleosome, thus indicating an involvement of this region in chromatin assembly. 相似文献
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Gregory B. Noe Meghan Q.N. Fellows Lorraine Parsons Janelle West John Callaway Sally Trnka Mark Wegener Joy Zedler 《Restoration Ecology》2019,27(4):750-757
In theory, extirpated plant species can be reintroduced and managed to restore sustainable populations. However, few reintroduced plants are known to persist for more than a few years. Our adaptive‐management case study illustrates how we restored the endangered hemiparasitic annual plant, Chloropyron maritimum subsp. maritimum (salt marsh bird's beak), to Sweetwater Marsh, San Diego Bay National Wildlife Refuge, California, United States, and used monitoring and experimentation to identify the factors limiting the reintroduced population. After extirpation in 1988, reintroduction starting that year led to a resilient, genetically diverse population in 2016 (a “boom” of approximately 14,000) that rebounded from a “bust” (62 in 2014). Multiple regressions attributed 82% of the variation in population counts to tidal amplitude, rainfall, and temperature. Populations of salt marsh bird's beak crashed when the diurnal tide range peaked during the 18.6‐year lunar nodal cycle (a rarely considered factor that periodically added approximately 12 cm to tidal ranges). We explain booms as follows: During smaller tidal amplitudes, above‐average rainfall could desalinize upper intertidal soils and stimulate salt marsh bird's beak germination. Then, moderate temperature in May favors growth to reproduction in June. In addition, salt marsh bird's beak needs a short and open canopy of native perennial plants, with roots to parasitize (not non‐native annual grass pseudohosts) and nearby upland soil for a preferred pollinator, ground‐burrowing bees. Although our reintroduced salt marsh bird's beak population is an exceptional case of persistence, this rare species‐specific environmental and biological requirement makes it vulnerable to rising sea levels and global warming. 相似文献
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Forest P. Hayes Joshua J. Millspaugh Eric J. Bergman Ragan M. Callaway Chad J. Bishop 《The Journal of wildlife management》2022,86(2):e22175
Across much of North America, populations of moose (Alces alces) are declining because of disease, predation, climate change, and anthropogenic-driven habitat loss. Contrary to this trend, populations of moose in Colorado, USA, have continued to grow. Studying successful (i.e., persistent or growing) populations of moose can facilitate continued conservation by identifying habitat features critical to persistence of moose. We hypothesized that moose using habitat with higher quality willow (Salix spp.) would have a higher probability of having a calf-at-heel (i.e., calving success). We evaluated moose calving success using repeated ground observations of collared individuals with calves in an occupancy model framework to account for detection probability. We then evaluated the impact of willow habitat quality and nutrition on moose calving success by studying 2 spatially segregated populations of moose in Colorado. Last, we evaluated correlations between willow characteristics (browse intensity, height, cover, leaf length, and species) and willow nutrition (dry matter digestibility [DMD]) to assess the utility of using those characteristics to assess willow nutrition. We found willow height and cover had a high probability of being positively associated with higher individual-level calving success. Willow DMD, browse intensity, and leaf length were not predictive of individual moose calving success; however, the site with higher mean DMD consistently had higher mean estimates of calving success for the same year. Our results suggest surveying DMD is likely not a useful metric for assessing differences in calving success of individual moose but may be of use at population levels. Further, the assessment of willow morphology and density may be used to identify areas that support higher levels of moose calving success. 相似文献
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Slate Mandy L. Matallana-Mejia Nicolas Aromin Alessandra Callaway Ragan M. 《Biological invasions》2022,24(10):3109-3118
Biological Invasions - Temporally dynamic resource supplies may alter or lead to fluctuations in competitive outcomes. Resource pulses have been theorized to promote incursion by exotic species... 相似文献
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Jonathan M. Adams Wei Fang Ragan M. Callaway Don Cipollini Elizabeth Newell 《Biological invasions》2009,11(4):1005-1016
Acer platanoides (Norway maple) is a widespread native tree species in Europe. It has been introduced to North America where it has often
established dense stands in both secondary woodlands and relatively undisturbed mature woodlands. In Europe A. platanoides is also extending its original range, but generally seems to exist at much lower densities. One explanation for the ‘aggressiveness’
of invasive plants such as A. platanoides is that they have left behind pests and diseases which limit their population densities in their native lands (the enemy
release hypothesis or ERH). To assess the ERH for Norway maple, a large network of collaborators assessed leaf herbivory rates
in populations throughout Europe and North America. We found significantly lower total leaf herbivory (1.6% ± 0.19, n = 21 vs. 7.4% ± 1.94, n = 34) and lower fungal damage (1.0% ± 0.35, n = 13 vs. 3.7% ± 0.85, n = 34) in North America than in Europe over a 2 year period, which is consistent with the predictions of the Enemy Release
Hypothesis. Across years, the average total leaf herbivory was significantly correlated with average annual temperature of
the site (P < 0.05), although this was mostly due to sites in Europe (P < 0.001), and not sites in North America (P > 0.05). Furthermore, only populations in Europe showed very high levels of herbivory (e.g., nine sites had total leaf herbivory
ranging from 10.0 to 51.2% in at least 1 year) or leaf fungal damage (only one site in North America showed high levels of
fungal damage in 1 year), suggesting the possibility of more frequent episodic outbreaks in the native range. Leaf herbivory
and fungal damage are only two aspects of consumer pressure and we do not know whether the differences reported here are enough
to actually elicit release from top-down population control, but such large scale biogeographic differences in herbivory contribute
towards understanding exotic invasions.
Jonathan M. Adams and Wei Fang—equally contributed as first authors.
A list of the participating members of the Transatlantic Acer platanoides Invasion Network is given in the Appendix 3. 相似文献
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Boris F. Krasnikov Chin-Hsiang Chien Regina Nostramo John T. Pinto Edward Nieves Myrasol Callaway Jin Sun Kay Huebner Arthur J.L. Cooper 《Biochimie》2009,91(9):1072-1080
The present report identifies the enzymatic substrates of a member of the mammalian nitrilase-like (Nit) family. Nit2, which is widely distributed in nature, has been suggested to be a tumor suppressor protein. The protein was assumed to be an amidase based on sequence homology to other amidases and on the presence of a putative amidase-like active site. This assumption was recently confirmed by the publication of the crystal structure of mouse Nit2. However, the in vivo substrates were not previously identified. Here we report that rat liver Nit2 is ω-amidodicarboxylate amidohydrolase (E.C. 3.5.1.3; abbreviated ω-amidase), a ubiquitously expressed enzyme that catalyzes a variety of amidase, transamidase, esterase and transesterification reactions. The in vivo amidase substrates are α-ketoglutaramate and α-ketosuccinamate, generated by transamination of glutamine and asparagine, respectively. Glutamine transaminases serve to salvage a number of α-keto acids generated through non-specific transamination reactions (particularly those of the essential amino acids). Asparagine transamination appears to be useful in mitochondrial metabolism and in photorespiration. Glutamine transaminases play a particularly important role in transaminating α-keto-γ-methiolbutyrate, a key component of the methionine salvage pathway. Some evidence suggests that excess α-ketoglutaramate may be neurotoxic. Moreover, α-ketosuccinamate is unstable and is readily converted to a number of hetero-aromatic compounds that may be toxic. Thus, an important role of ω-amidase is to remove potentially toxic intermediates by converting α-ketoglutaramate and α-ketosuccinamate to biologically useful α-ketoglutarate and oxaloacetate, respectively. Despite its importance in nitrogen and sulfur metabolism, the biochemical significance of ω-amidase has been largely overlooked. Our report may provide clues regarding the nature of the biological amidase substrate(s) of Nit1 (another member of the Nit family), which is a well-established tumor suppressor protein), and emphasizes a) the crucial role of Nit2 in nitrogen and sulfur metabolism, and b) the possible link of Nit2 to cancer biology. 相似文献