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31.
Lumphocytes were pulse-labelled with [3H] thymidine. Following G-banding, the cells were autoradiographed and 46 in their third post-labelling division selected. The locations of 611 sister-chromatid exchanges (SCE's) which had occurred in the previous two cell cycles were recorded as label discontinuities along identified chromosomes. Between particular chromosomes, SCE frequency was proportional to chromosome length. SCE frequency distributions within particular chromosomes fitted Poisson expectations. There was no over-representation of exchanges in centromeric regions, or in the C-banded regions of chromosomes 1, 9 and 16. A trend of increased frequency of SCE in darkly G-banded regions and in relatively darkly banded chromosomes was evident. The apparent excess of SCE in dark G-bands could be considered to be a consequence of the more condensed state of the DNA in these regions in the interphase nucleus relative to the DNA in pale G-band regions. Such compaction could result in an enhanced probability of SCE and a reduced probability of gross inter- or intra-change involving these regions. In contrast, the more extended interphase state of the DNA in pale G-banded regions would allow non-homologous exchange and account for the preferred location of X-ray-induced exchange events to pale G-bands. 相似文献
32.
Linkage of Six Genes in Chlamydomonas reinhardtii and the Construction of Linkage Test Strains 下载免费PDF全文
Linkage relationships were determined for six genes in Chlamydomonas reinhardtii: pyr, act, can-la, ey, y-1, and nic-7. Four of these were combined with five other genes to form linkage test strains. 相似文献
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The oligosaccharide units of rabbit immunoglobulin G. Asymmetric attachment of C2-oligosaccharide 总被引:2,自引:1,他引:1 下载免费PDF全文
Two populations of immunoglobulin G (IgG) molecules were isolated from pooled rabbit serum. The first was almost devoid of galactosamine and was obtained in a yield of 7% of the total IgG; the second contained on average a single residue of galactosamine per molecule and was obtained in a yield of 30% of the total IgG. The galactosamine, which is present solely in the C2-oligosaccharide, appeared to be present on one H-chain and not the other in the four-chain structure. Evidence was obtained by the isolation of a glycopeptide linked through a disulphide bridge to a second peptide of the same sequence; the oligosaccharide attached to the first peptide was absent from the complementary peptide. Further evidence was obtained by degradation and analysis of the 5S IgG fragment, which comprises an intact half-molecule coupled through a disulphide bridge to the Fc fragment derived from the opposing half molecule (Goodman, 1965); only the intact H-chain carried the C2-oligosaccharide. 相似文献
35.
Katrin Schmidt Antony J. Birchill Angus Atkinson Robert J. W. Brewin James R. Clark Anna E. Hickman David G. Johns Maeve C. Lohan Angela Milne Silvia Pardo Luca Polimene Tim J. Smyth Glen A. Tarran Claire E. Widdicombe E. Malcolm S. Woodward Simon J. Ussher 《Global Change Biology》2020,26(10):5574-5587
Continental margins are disproportionally important for global primary production, fisheries and CO2 uptake. However, across the Northeast Atlantic shelves, there has been an ongoing summertime decline of key biota—large diatoms, dinoflagellates and copepods—that traditionally fuel higher tropic levels such as fish, sea birds and marine mammals. Here, we combine multiple time series with in situ process studies to link these declines to summer nutrient stress and increasing proportions of picophytoplankton that can comprise up to 90% of the combined pico‐ and nanophytoplankton biomass in coastal areas. Among the pico‐fraction, it is the cyanobacterium Synechococcus that flourishes when iron and nitrogen resupply to surface waters are diminished. Our field data show how traits beyond small size give Synechococcus a competitive edge over pico‐ and nanoeukaryotes. Key is their ability to grow at low irradiances near the nutricline, which is aided by their superior light‐harvesting system and high affinity to iron. However, minute size and lack of essential biomolecules (e.g. omega‐3 polyunsaturated fatty acids and sterols) render Synechococcus poor primary producers to sustain shelf sea food webs efficiently. The combination of earlier spring blooms and lower summer food quantity and quality creates an increasing period of suboptimal feeding conditions for zooplankton at a time of year when their metabolic demand is highest. We suggest that this nutrition‐related mismatch has contributed to the widespread, ~50% decline in summer copepod abundance we observe over the last 60 years. With Synechococcus clades being prominent from the tropics to the Arctic and their abundances increasing worldwide, our study informs projections of future food web dynamics in coastal and shelf areas where droughts and stratification lead to increasing nutrient starvation of surface waters. 相似文献
36.
David M. Smyth Nicholas S. Horne Elli Ronayne Rachel V. Millar Patrick W. S. Joyce Maria Hayden‐Hughes Louise Kregting 《Restoration Ecology》2020,28(3):645-654
Ostrea edulis was once prolific throughout Europe and considered as the continent's native oyster. However, O. edulis currently exists in small fragmented assemblages where natural unaided recovery is rarely encountered. This research identified the small semi‐enclosed sea Lough of Strangford on the northeast coast of Northern Ireland as one of the few locations within Europe where the native oyster displayed gregarious natural rejuvenation. On close examination, four influential parameters appeared to assist in concentrated settlement; raised topographical cultch formations, shell coverage, the number of fecund in situ adults, and site protection. If these components were to be combined and managed as part of reintroduction and restoration initiatives, high‐density settlements and self‐sustaining populations may be possible. The research also identified that unregulated harvesting of intertidal O. edulis assemblages has the potential to seriously hinder natural recoveries. Indeed, the findings suggest that a review of policy in regards to intertidal hand gathering is necessary. However, naturally occurring high‐density settlements recorded during this research should be inspirational to all involved in the restoration of the native oyster. 相似文献
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Christophe J. Queval Antony Fearns Laure Botella Alicia Smyth Laura Schnettger Morgane Mitermite Esen Wooff Bernardo Villarreal-Ramos Waldo Garcia-Jimenez Tiaan Heunis Matthias Trost Dirk Werling Francisco J. Salguero Stephen V. Gordon Maximiliano G. Gutierrez 《PLoS pathogens》2021,17(3)
The Mycobacterium tuberculosis complex (MTBC) is a group of related pathogens that cause tuberculosis (TB) in mammals. MTBC species are distinguished by their ability to sustain in distinct host populations. While Mycobacterium bovis (Mbv) sustains transmission cycles in cattle and wild animals and causes zoonotic TB, M. tuberculosis (Mtb) affects human populations and seldom causes disease in cattle. The host and pathogen determinants underlying host tropism between MTBC species are still unknown. Macrophages are the main host cell that encounters mycobacteria upon initial infection, and we hypothesised that early interactions between the macrophage and mycobacteria influence species-specific disease outcome. To identify factors that contribute to host tropism, we analysed blood-derived primary human and bovine macrophages (hMϕ or bMϕ, respectively) infected with Mbv and Mtb. We show that Mbv and Mtb reside in different cellular compartments and differentially replicate in hMϕ whereas both Mbv and Mtb efficiently replicate in bMϕ. Specifically, we show that out of the four infection combinations, only the infection of bMϕ with Mbv promoted the formation of multinucleated giant cells (MNGCs), a hallmark of tuberculous granulomas. Mechanistically, we demonstrate that both MPB70 from Mbv and extracellular vesicles released by Mbv-infected bMϕ promote macrophage multinucleation. Importantly, we extended our in vitro studies to show that granulomas from Mbv-infected but not Mtb-infected cattle contained higher numbers of MNGCs. Our findings implicate MNGC formation in the contrasting pathology between Mtb and Mbv for the bovine host and identify MPB70 from Mbv and extracellular vesicles from bMϕ as mediators of this process. 相似文献
39.
Zhaoda Zhang Jean A. Smith Adrienne P. Smyth Warren Eisenberg Alexandra Nichols Gregory S. Pari 《Nucleosides, nucleotides & nucleic acids》2013,32(7-9):1169-1172
Abstract Several thiono triester containing oligonucleotide phosphorothioates linked with a lipophilic group have been synthesized. Some of these modified antisense oligonucleotides show potent anti-HCMV activity as well as improved cellular association and nuclease resistance. 相似文献
40.