Control of variant surface glycoprotein gene-expression sites in Trypanosoma brucei
Control of variant surface glycoprotein gene-expression sites in Trypanosoma brucei
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DOI：
10.1093/emboj/18.17.4846
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发表时间：
1999-09-01
期刊：
影响因子：
11.4
通讯作者：
Borst, P
中科院分区：
文献类型：
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作者：
Chaves, I;Rudenko, G;Borst, P
布鲁氏锥虫有20个类似的端粒表达位点，用于不同的表面糖蛋白基因。表达位点似乎在转录起始水平上受到控制，导致在任何时候只有一个位点是活跃的。在表达位点之间发生突变的几率很低。为了分析切换机制，我们使用了两个表达位点标记有两种不同耐药基因的锥虫，并将它们选择在含有两种药物的琼脂糖板上。双抗性克隆以每细胞10（-7）个的低频率出现，但它们表现得好像在两个标记的表达位点之间迅速切换，在没有选择的情况下失去了双抗性。通过原位杂交，我们发现只有10%的双耐药细胞有两个与转录表达位点对应的荧光点。我们的研究结果表明：(i)双表达子在表达位点突变中不是一个稳定的中间体；（ii）表达位点不能独立开启和关闭；（iii）表达位点可能处于“预激活”沉默状态，因此它们很容易被激活。
Trypanosoma brucei has 20 similar telomeric-expression sites for variant surface glycoprotein genes. Expression sites appear to be controlled at the level of transcription initiation, resulting in only one site being active at any time. Snitching between expression sites occurs at a low rate. To analyse the switching mechanism, we used trypanosomes with two expression sites tagged with two different drug-resistance genes and selected these on agarose plates containing both drugs. Double-resistant clones arose at a low frequency of 10(-7) per cell, but these behaved as if they rapidly switched between the two tagged expression sites and lost double resistance in the absence of selection. Using in situ hybridization we found that only 10% of the double-resistant cells had tno fluorescent spots corresponding to transcribed expression sites. Our results suggest that: (i) a double expressor is not a stable intermediate in expression site snitching; (ii) expression sites are not independently switched on and off; and (iii) expression sites can be in a 'pre-active' silent state from which they can be readily activated.