Establishment and maintenance of a heterochromatin domain     

Hall IM  Shankaranarayana GD  Noma K  Ayoub N  Cohen A  Grewal SI 《Science (New York, N.Y.)》2002,297(5590):2232-2237

The higher-order assembly of chromatin imposes structural organization on the genetic information of eukaryotes and is thought to be largely determined by posttranslational modification of histone tails. Here, we study a 20-kilobase silent domain at the mating-type region of fission yeast as a model for heterochromatin formation. We find that, although histone H3 methylated at lysine 9 (H3 Lys9) directly recruits heterochromatin protein Swi6/HP1, the critical determinant for H3 Lys9 methylation to spread in cis and to be inherited through mitosis and meiosis is Swi6 itself. We demonstrate that a centromere-homologous repeat (cenH) present at the silent mating-type region is sufficient for heterochromatin formation at an ectopic site, and that its repressive capacity is mediated by components of the RNA interference (RNAi) machinery. Moreover, cenH and the RNAi machinery cooperate to nucleate heterochromatin assembly at the endogenous mat locus but are dispensable for its subsequent inheritance. This work defines sequential requirements for the initiation and propagation of regional heterochromatic domains.  相似文献   

Containing pandemic influenza at the source   总被引：1，自引：0，他引：1  

Longini IM  Nizam A  Xu S  Ungchusak K  Hanshaoworakul W  Cummings DA  Halloran ME 《Science (New York, N.Y.)》2005,309(5737):1083-1087

Highly pathogenic avian influenza A (subtype H5N1) is threatening to cause a human pandemic of potentially devastating proportions. We used a stochastic influenza simulation model for rural Southeast Asia to investigate the effectiveness of targeted antiviral prophylaxis, quarantine, and pre-vaccination in containing an emerging influenza strain at the source. If the basic reproductive number (R0) was below 1.60, our simulations showed that a prepared response with targeted antivirals would have a high probability of containing the disease. In that case, an antiviral agent stockpile on the order of 100,000 to 1 million courses for treatment and prophylaxis would be sufficient. If pre-vaccination occurred, then targeted antiviral prophylaxis could be effective for containing strains with an R0 as high as 2.1. Combinations of targeted antiviral prophylaxis, pre-vaccination, and quarantine could contain strains with an R(0) as high as 2.4.  相似文献   

Antimicrobial ability and growth promoting effects of feed supplemented with probiotic bacterium isolated from gut microflora of Cirrhinus mrigala     

Anita Bhatnagar  Ritu Lamba 《中国农业科学(英文版)》2015,(3):583-592

The present studies were conducted to isolate, select, identify and characterize gut bacteria as antimicrobial and growth promoting agent for the feed of economically important fish Cirrhinus mrigala. Intestinal microflora were isolated, counted, and identified, and their in vitro antibacterial properties were determined. The results have revealed that occurrence of Gram-negative rods was around 75% and of Gram-positive rods was 25%. Among the isolates Gram-positive were maintained in nutrient agar slants at 4°C. Of these, eight strains were replica-plated on agar seeded with Aeromonas hydrophila and only one strain CM2(C. mrigala 2) exhibited antibacterial properties in vitro showing inhibition against fish pathogen by well diffusion assay. This isolated strain was identified as Bacillus cereus. This bacterium was mass cultured and incorporated in the pelleted diet(40% protein and 18 k J g–1 gross energy) of C. mrigala to investigate its effect on growth performance, digestibility, nutrient retention and activities of digestive enzymes. The results of feeding trial revealed significantly(P<0.05) high growth performance in terms of specific growth rate, growth percent gain in body weight(BD)(272.4±1.5)%, high apparent protein digestibility((79.9±0.30)%) and low food conversion ratio in the group of fishes fed on diet containing B. cereus in comparison to the fishes fed on diet without probiotics. The carcass composition also revealed high accumulation of proteins((15.28±0.15) g 100 g–1) in fishes fed on diet containing probiotics. Intestinal enzyme activities of protease, amylase and cellulase were also significantly(P<0.05) high in the group of fishes fed on diet supplemented with probiotics indicating the extracellular enzyme production by B. cereus. These results indicate that probiotics stimulate the digestion through the supply of digestive enzyme and certain essential nutrients to animals. Also significantly(P<0.05) low excretion of metabolites, i.e., ammonia excretion and phosphate production(mg kg–1 BW d–1) was observed in the fishes fed with probiotic based diets. Thus, B. cereus appears to be a promising candidate for ptobiotic applications which can enhance growth performance and nutrient retention in C. mrigala.  相似文献