GENOMIC ENVIRONMENT OF THE EXPRESSION-LINKED EXTRA COPIES OF GENES FOR SURFACE-ANTIGENS OF TRYPANOSOMA-BRUCEI RESEMBLES THE END OF A CHROMOSOME
GENOMIC ENVIRONMENT OF THE EXPRESSION-LINKED EXTRA COPIES OF GENES FOR SURFACE-ANTIGENS OF TRYPANOSOMA-BRUCEI RESEMBLES THE END OF A CHROMOSOME
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DOI：
10.1038/299451a0
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发表时间：
1982-01-01
期刊：
影响因子：
64.8
通讯作者：
BORST, P
中科院分区：
文献类型：
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作者：
DELANGE, T;BORST, P
锥虫的表面涂层基本上由单一蛋白质组成，即变体表面糖蛋白（VSG）1，2。但是可以生产一百多种不同的VSG 3。通过从一种VSG的合成切换到下一种，锥虫改变其表面的抗原性质，从而逃避宿主免疫系统的破坏4 -6。每个VSG由一个单独的基因编码，其中一些基因的表达涉及沉默基本拷贝（BC）的复制和转座到一个新的基因组环境中7 -9，在那里基因被转录10，11。该基因的转座表达连锁额外拷贝（ELC）下游的DNA片段具有两个显著特性。它缺乏一段7个限制性内切酶（kb）的限制性内切酶切割位点，该限制性内切酶切割位点突然终止于至少17个限制性内切酶切割位点的明显簇。在这里，我们表明，在完整的DNA中，两个活性VSG基因的“贫瘠”区域3′优先受到核酸外切酶Bal 31的攻击。我们的结论是，这些基因的表达拷贝位于邻近的DNA中的不连续性，大概是染色体的末端。
The surface coat of trypanosomes consists essentially of a single protein, the variant surface glycoprotein (VSG)1,2. But more than a hundred different VSGs can be produced3. By switching from the synthesis of one VSG to the next, trypanosomes change the antigenic nature of their surface and thus escape destruction by the host immune system4–6. Each VSG is encoded by a separate gene and expression of some of these genes involves the duplication and transposition of a silent basic copy (BC) into a new genomic environment7–9, where the gene is transcribed10,11. The DNA segment downstream of this transposed expression-linked extra copy (ELC) of the gene has two remarkable properties. It is devoid of restriction endonuclease cutting sites for a stretch of 7 kilobases (kb) which ends abruptly in an apparent cluster of at least 17 restriction endonuclease cutting sites. Here we show that in intact DNA the ‘barren’ region 3′ to two active VSG genes is preferentially attacked by exonucleaseBal31. We conclude that the expressed copies of these genes are located adjacent to a discontinuity in the DNA, presumably the end of a chromosome.