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首页> 外文期刊>Infection and immunity >Isolation and molecular characterization of spontaneously occurring cytolysin-negative mutants of Actinobacillus pleuropneumoniae serotype 7.
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Isolation and molecular characterization of spontaneously occurring cytolysin-negative mutants of Actinobacillus pleuropneumoniae serotype 7.

机译：胸膜肺炎放线杆菌血清型7自发发生的细胞溶素阴性突变体的分离和分子鉴定。

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摘要

Actinobacillus pleuropneumoniae serotype 7 strains are shown to spontaneously lose cytolytic activity with a frequency of approximately 10(-4). The phenotypic change is associated with the loss of approximately 8.5 kbp of chromosomal DNA. A genomic fragment encoding the cytolysin and its flanking sequences was cloned and characterized. Also, the corresponding truncated fragment was cloned from a spontaneous mutant. Comparison of the two clones allowed the definition of the excision site. The ends of the excised fragment are composed of 1,201 bp long direct identical repeats, possibly facilitating the genotypic change by homologous recombination. In accordance with this hypothesis, one repeat is conserved in the spontaneous mutant. Each repeat contains one open reading frame preceded by a Shine-Dalgarno consensus sequence, and the ends of each repeat contain 26-bp complementary sequences with four mismatches.
机译：胸膜肺炎放线杆菌血清型7菌株显示自发丧失细胞溶解活性，频率约为10（-4）。表型的变化与染色体DNA约8.5 kbp的丢失有关。克隆并鉴定了编码细胞溶素及其侧翼序列的基因组片段。同样，从自发突变体克隆相应的截短的片段。比较两个克隆可以确定切除位点。切除的片段的末端由1,201 bp长的直接相同重复序列组成，可能通过同源重组促进基因型改变。根据这一假设，自发突变体中一个重复序列是保守的。每个重复序列包含一个开放阅读框，前面是Shine-Dalgarno共有序列，每个重复序列的末端包含具有四个错配的26 bp互补序列。

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