Hoover T A, Vodkin M H, Williams J C
Bacteriology Division, U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, Maryland 21702-5011.
J Bacteriol. 1992 Sep;174(17):5540-8. doi: 10.1128/jb.174.17.5540-5548.1992.
A DNA fragment located on the 3' side of the Coxiella burnetii htpAB operon was determined by Southern blotting to exist in approximately 19 copies in the Nine Mile I genome. The DNA sequences of this htpAB-associated repetitive element and two other independent copies were analyzed to determine the size and nature of the element. The three copies of the element were 1,450, 1,452, and 1,458 bp long, with less than 2% divergence among the three sequences. Several features characteristic of bacterial insertion sequences were discovered. These included a single significant open reading frame that would encode a 367-amino-acid polypeptide which was predicted to be highly basic, to have a DNA-binding helix-turn-helix motif, to have a leucine zipper motif, and to have homology to polypeptides found in several other bacterial insertion sequences. Identical 7-bp inverted repeats were found at the ends of all three copies of the element. However, duplications generated by many bacterial mobile elements in the recipient DNA during insertion events did not flank the inverted repeats of any of the three C. burnetii elements examined. A second pair of inverted repeats that flanked the open reading frame was also found in all three copies of the element. Most of the divergence among the three copies of the element occurred in the region between the two inverted repeat sequences in the 3' end of the element. Despite the sequence changes, all three copies of the element have retained significant dyad symmetry in this region.
通过Southern印迹法确定，位于伯纳特立克次氏体htpAB操纵子3'端的一个DNA片段在九英里I型基因组中约以19个拷贝存在。对这个与htpAB相关的重复元件的DNA序列以及另外两个独立拷贝进行了分析，以确定该元件的大小和性质。该元件的三个拷贝长度分别为1450、1452和1458 bp，三个序列之间的差异小于2%。发现了几个细菌插入序列的特征。这些特征包括一个单一的重要开放阅读框，它将编码一个367个氨基酸的多肽，预计该多肽具有高度碱性，具有DNA结合螺旋-转角-螺旋基序、亮氨酸拉链基序，并且与其他几种细菌插入序列中发现的多肽具有同源性。在该元件的所有三个拷贝的末端都发现了相同的7 bp反向重复序列。然而，在插入事件中许多细菌移动元件在受体DNA中产生的重复序列并没有位于所检测的三个伯纳特立克次氏体元件中任何一个的反向重复序列两侧。在该元件的所有三个拷贝中还发现了位于开放阅读框两侧的第二对反向重复序列。该元件的三个拷贝之间的大部分差异发生在元件3'端两个反向重复序列之间的区域。尽管存在序列变化，但该元件的所有三个拷贝在该区域都保留了显著的二元对称性。
