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951.
记述了在山东省五图盆地下始新统发现的一种“伪齿兽集目”化石 :千禧福兽 (Olbither iummillenariusumgen.etsp .nov.)。千禧福兽其颊齿形态基本上与原始奇蹄类相似 ,同时也具有伪齿兽类的一些特征 ,如m1~ 2下次尖没有与下内尖直接连接的下次脊。千禧福兽的M3次尖具前、后棱 ,这一点似与原始的蹄兔Seggeurius相似。因此 ,新种在目一级的归类有困难 ,暂置于McKenna ( 1 975 )创立的“伪齿兽集目”(“MirorderPhenacodonta”)。千禧福兽的发现进一步证明了奇蹄类可能起源于亚洲和北非类似伪齿兽类 (phenacodontids)的古有蹄类 ,福兽仅是类似伪齿兽类的古新世古有蹄类向奇蹄类进化过程中的一叉支的代表。 相似文献
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954.
Identification and Characterization of Shiga Toxin Type 2 Variants in Escherichia coli Isolates from Animals, Food, and Humans 下载免费PDF全文
Jie Zheng Shenghui Cui Louise D. Teel Shaohua Zhao Ruby Singh Alison D. O'Brien Jianghong Meng 《Applied microbiology》2008,74(18):5645-5652
There is considerable heterogeneity among the Shiga toxin type 2 (Stx2) toxins elaborated by Shiga toxin-producing Escherichia coli (STEC). One such Stx2 variant, the Stx2d mucus-activatable toxin (Stx2dact), is rendered more toxic by the action of elastase present in intestinal mucus, which cleaves the last two amino acids of the A2 portion of the toxin A subunit. We screened 153 STEC isolates from food, animals, and humans for the gene encoding Stx2dact by using a novel one-step PCR procedure. This method targeted the region of stx2dact that encodes the elastase recognition site. The presence of stx2dact was confirmed by DNA sequencing of the complete toxin genes. Seven STEC isolates from cows (four isolates), meat (two isolates), and a human (one isolate) that carried the putative stx2dact gene were identified; all were eae negative, and none was the O157:H7 serotype. Three of the isolates (CVM9322, CVM9557, and CVM9584) also carried stx1, two (P1332 and P1334) carried stx1 and stx2c, and one (CL-15) carried stx2c. One isolate, P1130, harbored only stx2dact. The Vero cell cytotoxicities of supernatants from P1130 and stx1 deletion mutants of CVM9322, CVM9557, and CVM9584 were increased 13- to 30-fold after treatment with porcine elastase. Thus, Stx2dact-producing strains, as detected by our one-step PCR method, can be isolated not only from humans, as previously documented, but also from food and animals. The latter finding has important public health implications based on a recent report from Europe of a link between disease severity and infection with STEC isolates that produce Stx2dact. 相似文献
955.
A Novel Gene, Encoding 6-Hydroxy-3-Succinoylpyridine Hydroxylase, Involved in Nicotine Degradation by Pseudomonas putida Strain S16 下载免费PDF全文
Hongzhi Tang Shuning Wang Lanying Ma Xiangzhou Meng Zixin Deng Dake Zhang Cuiqing Ma Ping Xu 《Applied microbiology》2008,74(5):1567-1574
Previous research suggested that Pseudomonas spp. may attack the pyrrolidine ring of nicotine in a way similar to mammalian metabolism, resulting in the formation of pseudooxynicotine, the direct precursor of a potent tobacco-specific lung carcinogen. In addition, the subsequent intermediates, 6-hydroxy-3-succinoylpyridine (HSP) and 2,5-dihydroxypyridine (DHP) in the Pseudomonas nicotine degradation pathway are two important precursors for drug syntheses. However, there is little information on the molecular mechanism for nicotine degradation via the pyrrolidine pathway until now. In this study we cloned and sequenced a 4,879-bp gene cluster involved in nicotine degradation. Intermediates N-methylmyosmine, pseudooxynicotine, 3-succinoylpyridine, HSP, and DHP were identified from resting cell reactions of the transformant containing the gene cluster and shown to be identical to those of the pyrrolidine pathway reported in wild-type strain Pseudomonas putida S16. The gene for 6-hydroxy-3-succinoylpyridine hydroxylase (HSP hydroxylase) catalyzing HSP directly to DHP was cloned, sequenced, and expressed in Escherichia coli, and the purified HSP hydroxylase (38 kDa) is NADH dependent. DNA sequence analysis of this 936-bp fragment reveals that the deduced amino acid shows no similarity with any protein of known function. 相似文献
956.
中国对虾(Penaeus chinensis)4个种群的同工酶遗传变异 总被引:23,自引:0,他引:23
采用水平淀粉凝胶电泳技术分析了中国对虾(Penaeuschinensis)黄渤海沿岸种群(YP)、朝鲜半岛西海岸种群(KP)和2个养殖种群(CP1和CP2)的同工酶遗传变异水平。每个种群随机选取50尾中国对虾进行同工酶检测。在所分析的12种同工酶编码的20个基因位点中,有4个是多态位点。4个种群的多态位点比例(P0.99)分别为15%、20%、10%和20%。种群平均杂合度(观测值)(Ho)分别为0.014±0.007、0.020±0.010、0.010±0.007和0.033±0.017。4个种群的位点有效等位基因数(Ne)分别为1.015±0.008、1.023±0.011、1.011±0.007和1.042±0.022。杂合子平衡偏离指数(D)分别为+0.037、-0.030、-0.098和-0.030。2个地理种群(YP和KP)的遗传相似性系数(I)和遗传距离(D 相似文献
957.
马齿苋Portulaca oleracea是常用的药食兼用植物。本文对其药、食用价值及开发前景作了综述,并对其栽培条件作了初步的研究。 相似文献
958.
The E3 ligase HERC4 is overexpressed in human breast cancer and its expression levels correlated with the prognosis of breast cancer patients. However, the roles of HERC4 in mammary tumorigenesis remain unclear. Here we demonstrate that the knockdown of HERC4 in human breast cancer cells dramatically suppressed their proliferation, survival, migration, and tumor growth in vivo, while the overexpression of HERC4 promoted their aggressive tumorigenic activities. HERC4 is a new E3 ligase for the tumor suppressor LATS1 and destabilizes LATS1 by promoting the ubiquitination of LATS1. miRNA-136-5p and miRNA-1285-5p, expression of which is decreased in human breast cancers and is inversely correlated with the prognosis of breast cancer patients, are directly involved in suppressing the expression of HERC4. In summary, we discover a miRNA-HERC4-LATS1 pathway that plays important roles in the pathogenesis of breast cancer and represents new therapeutic targets for human breast cancer. 相似文献
959.
安徽两种蜜蜂种群的春季繁殖及数量动态特征 总被引:11,自引:4,他引:7
1997~ 1999年在皖中和皖西、皖南山区对意大利蜜蜂 (ApismelliferaLigusticaSpi.)和中华蜜蜂(ApisceranaceranaFeb .)种群数量动态进行系统观察研究 .结果表明 ,蜜蜂种群数量明显受气候和蜜粉源植物的影响 ,周年呈现“两高”(春、秋 )和两低 (夏、冬 )的变化模式曲线 ;意大利蜜蜂春繁及秋季更新速度明显快于中华蜜蜂 ,但越夏效果不及中华蜜蜂 .意大利蜜蜂的性比值为 (314.4± 2 89.9)∶1~ (32 9.4± 30 5 .8)∶1,中华蜜蜂为 (334.2± 2 35 .5 )∶1~ (413 .1± 377.2 )∶1,雄蜂呈季节性出现 .蜜蜂种群内年龄组配在不断变化 . 相似文献
960.
Jess M Cunnick Songshu Meng Yuan Ren Caroline Desponts Hong-Gang Wang Julie Y Djeu Jie Wu 《The Journal of biological chemistry》2002,277(11):9498-9504
Gab1-SHP2 association is required for Erk mitogen-activated protein kinase activation by several growth factors. Gab1-SHP2 interaction activates SHP2. However, an activated SHP2 still needs to associate with Gab1 to mediate Erk activation. It was unclear whether SHP2 is required to dephosphorylate a negative phosphorylation site on Gab1 or whether SHP2 needs the Gab1 pleckstrin homology (PH) domain to target it to the plasma membrane. We found that expression of a fusion protein consisting of the Gab1 PH domain and an active SHP2 (Gab1PH-SHP2DeltaN) induced constitutive Mek1 and Erk2 activation. Linking the active SHP2DeltaN to the PDK1 PH domain or the FRS2beta myristoylation sequence also induced Mek1 activation. Mek1 activation by Gab1PH-SHP2DeltaN was inhibited by an Src inhibitor and by Csk. Significantly, Gab1PH-SHP2DeltaN induced Src activation. Gab1PH-SHP2DeltaN expression activated Ras, and the Gab1PH-SHP2DeltaN-induced Mek1 activation was blocked by RasN17. These findings suggest that Gab1PH-SHP2DeltaN activated a signaling step upstream of Src and Ras. The SHP2 tyrosine phosphatase activity is essential for the function of the fusion protein. Together, these data show that the Gab1 sequence, besides the PH domain and SHP2 binding sites, is dispensable for Erk activation, suggesting that the primary role of Gab1 association with an activated SHP2 is to target it to the membrane. 相似文献