MicroRNAs (miRNAs) are present in both plant and animal kingdoms and represents a growing family of non-coding RNAs. These tiny RNAs act as small guides and direct negative regulations usually in the process of development through sequence complementarity to target mRNAs. Although a large number of miRNAs have been identi?ed from various animals, so far plant miRNA studies have focused mainly on Arabidopsis. Here we describe the identification of 20 miRNAs from a rice cDNA library. All the miRNAs were presumably processed from precursors with stem±loop structures and were positively detected in rice cells from at least one tissue, some of which showed tissue-specific expression. Twenty-three unique rice genes were identified to be feasible targets for seven rice miRNAs, including four members of Scarecrow-like transcription factor, the targets of miR-39 that had been characterized in Arabidopsis. Lacking long complementarity, the regulatory targets of 13 miRNAs remain to be further investigated. A possible mechanism of translational repressor for plant miRNAs that lack perfect complementarity to target mRNAs is discussed.

To augment the immunogenicity of the subunit B of Shiga toxin (Stx2e B) produced by Escherichia coli and protect piglets from edema disease in china, a fusion gene was constructed consisting of Stx2e B genetically linked at the N-terminus of the B subunit of heat-labile enterotoxin (LTB) in a translational fusion. After being induced with IPTG, the expressed fusion protein of Stx2e B-LTB was about 8.8% of total proteins, approximately 13 mg/ml of the bacteria culture. The Stx2e B-LTB fusion protein was found to be nontoxic to Vero cells at the dose higher than 1 mg/ml and to mice less than 100 mg/ml. Antibody titer against the fusion protein Stx2e B-LTB was 1:76, 800, much higher than that of the recombinant Stx2e B protein (1:12, 800) alone. All of the mice immunized with the Stx2e B-LTB fusion protein survived when challenged with a lethal dose (LD) of Stx2e toxin. The results showed that the poor immunogenicity of Stx2e B was overcome by conjugating the stx2e B to ltB. The immunogenicity of the constructed fusion protein Stx2e B-LTB in the present study was highly qualified to protect animals against Shiga toxin produced from Shiga toxin-producing Escherichia coli (STEC). The fusion protein of Stx2e B-LTB could be a candidate for a vaccine against edema disease and post-weaning diarrhea simultaneously in piglets.

用聚合酶链反应扩增出猪源大肠杆菌编码ST前体（pro-ST）和Lt的B亚单位（LTB）成熟多肽的序列，再通过套式PcR将pro-ST编码序列3'端和LTB编码序列5’端融合，并置于同一词读框内，得到SL和LTB的融合基因，将此序列克隆到pGEM-T质粒中，序列分析后，亚克隆到表达载体pOE30中，在大肠杆菌细胞中得到表达，表达的融合蛋白同时具有田和LTB的抗原性，且无ST和LT的生物毒性。

从仔猪水肿病样品中分离的一株大肠杆菌菌株NP962l 抽提染色体DNA，构建NP962l 的总DNA文库，经菌落原位杂交筛选、限制酶酶切和southem 印迹等分析，获得含有志贺样毒素基因的重组质粒，核苷酸序列分析表明，该基因的A亚基与SLt-IIes的同源性为97.6%-98.1%，与SLT-IIc\SLT-IId及EHEc 0157:H7产生的SLT-II的A亚基之司的同源性分别为93.1%、93.0%和92。9%；B亚基与SLT-lles的同源性为99.62%-100%，与SLT-iiC\slt：IId及slt-II的同源性分别为81.5%、81.15和81.5%；与29种已知序列的SKT-II slt-i及志贺毒素stx进行聚类分析，结果证实大肠杆菌NP9621菌株中的志贺样毒素基因属于一种新的slt-II亚型。SLT-IIE/NP962l的A亚基与其它slt-IIe之司存在7-9个氨基酸的差异B亚基的氨基酸序列完全相同，与A亚基毒力活性密切相关的氨基酸分别为Thr4、Glu167 Arg170 和Arg176。

【目的】紫杉醇是重要的抗癌药物，主要从罗汉松等植物中提取，为了保护罗汉松等种质资源，本文从罗汉松植株中分离产紫杉醇内生真菌，并对内生真菌所产紫杉醇的抗肿瘤活性进行了分析。【方法】采用组织块法自罗汉松的根、茎、叶等组织中分离内生真菌：通过四唑蓝（Methvl ThlazolvlTetrazollum，MTT）比色法筛选有抗肿瘤活性的内生真菌菌株，通过薄层层析（Thln Laver chro-matography，TLc）和高效液相色谱（H1gh Performance L1quld chromatography，HPLc）对内生真菌所产活性物质进行鉴定：采用抽提法抽提内生真菌所产紫杉醇，应用vero细胞对抽提的紫杉醇的活性进行了分析。【结果】从罗汉松属（Podocrapus）植物中分离到155株内生真菌，其中28株内生真菌具有较高的抑癌活性。将其中一株菌株A2命名为EPTP-1，经形态学和分子分类学分析鉴定为烟曲霉（Aspergillus fumigatus）菌株EPTP-1中抽提的紫杉醇5.553ug/L～555.3ug/L作用24h表现出明显的致细胞凋亡作用。菌株EPTP-1发酵5天时紫杉醇的产率为0.5578±0.0294mg/L。【结论】从罗汉松中分离到了一株产紫杉醇内生真菌EPTP-1，可作为紫杉醇类药物工业化生产的候选菌株。