甲胎蛋白特异性小干扰RNA表达载体的构建及鉴定

目的：构建特异性抑制甲胎蛋白（AFP）的小干扰RNA（siRNA）表达载体,为进一步研究AFP基因功能及AFP相关肿瘤的基因治疗奠定基础。方法：设计并合成AFP特异性的短链寡核苷酸,退火形成双链DNA片段,通过与RNAi-Ready pSIREN-DNR-DsRed-Express Donor Vector连接、转化大肠杆菌、扩增、纯化得到所需质粒,用琼脂糖凝胶电泳及基因测序鉴定其分子量及插入片段的序列。结果：琼脂糖凝胶电泳证实纯化后的质粒大小约为6740bp,测序证实插入序列与合成的寡核苷酸序列完全符合。结论：构建了AFP特异性的siRNA表达质粒pSIREN-DNR—DsRed-Express Donor Vector-AFP。     

红芒6号果实成熟阶段香气成分研究

对商熟期及完熟期的红芒6号芒果果实采用顶空固相微萃取法(HS-SPME)提取香气成分,以气相色谱—质谱分析进行鉴定。共检出22种香气成分,其中商熟期14种,完熟期10种,主要为萜烯类、醛类、酸类等。两个阶段都具有的成分是α-桂叶烯、α-蛇麻烯等;商熟期主要的香气成分是( )-2-蒈烯;完熟期的主要香气成分是δ-3-蒈烯。     

Genetic constraints on protein evolution

Evolution requires the generation and optimization of new traits ("adaptation") and involves the selection of mutations that improve cellular function. These mutations were assumed to arise by selection of neutral mutations present at all times in the population. Here we review recent evidence that indicates that deleterious mutations are more frequent in the population than previously recognized and that these mutations play a significant role in protein evolution through continuous positive selection. Positively selected mutations include adaptive mutations, i.e. mutations that directly affect enzymatic function, and compensatory mutations, which suppress the pleiotropic effects of adaptive mutations. Compensatory mutations are by far the most frequent of the two and would allow potentially adaptive but deleterious mutations to persist long enough in the population to be positively selected during episodes of adaptation. Compensatory mutations are, by definition, context-dependent and thus constrain the paths available for evolution. This provides a mechanistic basis for the examples of highly constrained evolutionary landscapes and parallel evolution reported in natural and experimental populations. The present review article describes these recent advances in the field of protein evolution and discusses their implications for understanding the genetic basis of disease and for protein engineering in vitro.     

Identification of lactobacilli isolated from the cloaca and vagina of laying hens and characterization for potential use as probiotics to control Salmonella Enteritidis

AIMS: To select Lactobacillus strains from laying hens for potential use as probiotic to control Salmonella Enteritidis infection. METHODS AND RESULTS: One hundred and eighty-six lactobacilli were isolated from the cloaca and vagina of laying hens, and identified at the species level by a polyphasic taxonomic approach. All isolates belonged to the Lactobacillus acidophilus, Lactobacillus reuteri or Lactobacillus salivarius phylogenetic groups, with the L. reuteri group being the most predominant group. Based on genetic diversity, about 50 representative strains were selected and tested for in vitro properties that could be predictive for probiotic activity in laying hens. Salmonella inhibition was shown to be species dependent, and correlated to some extent with the production of lactic acid. A selection of strains was evaluated in a S. Enteritidis challenge experiment. Two strains, L. reuteri R-17485 and Lactobacillus johnsonii R-17504 significantly decreased the colonization of chicks by S. Enteritidis in caeca, liver and spleen. CONCLUSIONS: Lactobacilli isolated from laying hens were observed to inhibit Salmonella growth in vitro, most probably through production of lactic acid, and to decrease in vivo the S. Enteritidis colonization of chicks. SIGNIFICANCE AND IMPACT OF THE STUDY: The data demonstrate that Lactobacillus isolates from laying hens may have probiotic potential in reducing S. Enteritidis infection.     

1-甲基环丙烯(1-MCP)对'嘎拉'苹果贮藏期间果肉细胞结构的影响

在室温[(25±1)℃]条件下观察1-甲基环丙烯(1-MCP)影响下‘嘎拉’苹果采后果肉细胞结构变化的结果表明,随着贮藏时间的延长,未作1-MCP处理的果实果肉细胞逐渐失去张力,细胞壁皱褶,中胶层逐渐降解,继而出现胞间裂痕,细胞间隙逐渐增大,细胞壁纤维松散,细胞器逐渐空泡化等现象;1-MCP显著抑制果肉细胞的结构损伤,最终减缓果实的软化。