用已知遗传图位的BAC克隆片段，对水稻(Oryza sativa)小穗cDNA文库进行筛选，获 得一个水稻小GTP结合蛋白(small GTP-binding protein, SGP) 的相关序列，序列测定后 以该 cDNA序列为基础将4个表达序列标记(EST)进行了电子克隆(electronic cloning)，根据电子 克隆结果 设计引物，利用RT-PCR方法获得了一个水稻（Oryza sativa）中尚未鉴定的 cDNA 克隆Osrab5B，长1016bp。它与龙船海棠属（Mesembryanthemum crystallinum）和 百脉根属 （Lotus japonicus）命名为rab5B基因（序列登录号分别是AJ006225和Z73939）有着高 度同 源性（cDNA核苷酸序列ID值分别大于74%和76%），同属rab家族的一个新的亚族。进 而根据O srab5B的cDNA序列设计引物，扩增得到Osrab5B的基因组克隆，序列分析表明它至少 有7个内含子和8个外显子。%Small GTP-binding proteins (SGPs) are involved in regulating intracellular ve sicular transport by activation of vesicle formation and fusion of inner membran e. By means of screening a rice panicle cDNA library with one map position known genomic BAC clone as probe, an EST encoding a fragment of a SGP was obtained. B ased on the sequence of this EST, the electronic cloning was performed with anot her 3 ESTs. According to the result, the primers were designed and a cDNA clone was got, named Osrab5B, by means of RT-PCR. Osrab5B contains 1016 bp an d shows high similarity to the rab5B genes from Mesembryanthemum crytallinum and L otus j aponicus, all of which belong to a new subfamily of rab family. Further more, ne w primers were designed and the genomic sequence of Osrab5B was obtained. Ou r analysis indicates that it includes at least 7 introns and 8 exons.
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