Biessmann H, Valgeirsdottir K, Lofsky A, Chin C, Ginther B, Levis R W, Pardue M L
Developmental Biology Center, University of California, Irvine 92717.
Mol Cell Biol. 1992 Sep;12(9):3910-8. doi: 10.1128/mcb.12.9.3910-3918.1992.
Eight terminally deleted Drosophila melanogaster chromosomes have now been found to be "healed." In each case, the healed chromosome end had acquired sequence from the HeT DNA family, a complex family of repeated sequences found only in telomeric and pericentric heterochromatin. The sequences were apparently added by transposition events involving no sequence homology. We now report that the sequences transposed in healing these chromosomes identify a novel transposable element, HeT-A, which makes up a subset of the HeT DNA family. Addition of HeT-A elements to broken chromosome ends appears to be polar. The proximal junction between each element and the broken chromosome end is an oligo(A) tract beginning 54 nucleotides downstream from a conserved AATAAA sequence on the strand running 5' to 3' from the chromosome end. The distal (telomeric) ends of HeT-A elements are variably truncated; however, we have not yet been able to determine the extreme distal sequence of a complete element. Our analysis covers approximately 2,600 nucleotides of the HeT-A element, beginning with the oligo(A) tract at one end. Sequence homology is strong (greater than 75% between all elements studied). Sequence may be conserved for DNA structure rather than for protein coding; even the most recently transposed HeT-A elements lack significant open reading frames in the region studied. Instead, the elements exhibit conserved short-range sequence repeats and periodic long-range variation in base composition. These conserved features suggest that HeT-A elements, although transposable elements, may have a structural role in telomere organization or maintenance.
现已发现八条末端缺失的黑腹果蝇染色体已被“修复”。在每种情况下，修复后的染色体末端都获得了来自HeT DNA家族的序列，HeT DNA家族是一个复杂的重复序列家族，仅存在于端粒和着丝粒周围的异染色质中。这些序列显然是通过不涉及序列同源性的转座事件添加的。我们现在报告，在修复这些染色体过程中转座的序列鉴定出一种新型转座元件HeT-A，它构成了HeT DNA家族的一个子集。向断裂的染色体末端添加HeT-A元件似乎具有极性。每个元件与断裂的染色体末端之间的近端连接是一个寡聚（A）序列，从染色体末端5'到3'方向的链上保守的AATAAA序列下游54个核苷酸处开始。HeT-A元件的远端（端粒）末端有不同程度的截短；然而，我们尚未能够确定一个完整元件的最远端序列。我们的分析涵盖了HeT-A元件约2600个核苷酸，从一端的寡聚（A）序列开始。序列同源性很强（在所研究的所有元件之间大于75%）。序列可能是为了DNA结构而不是蛋白质编码而保守；即使是最近转座的HeT-A元件在所研究的区域也缺乏明显的开放阅读框。相反，这些元件表现出保守的短程序列重复和碱基组成的周期性长程变化。这些保守特征表明，HeT-A元件虽然是转座元件，但可能在端粒组织或维持中具有结构作用。
