Horn D, Cross G A
Laboratory of Molecular Parasitology, Rockefeller University, New York, New York 10021-6399, USA.
Cell. 1995 Nov 17;83(4):555-61. doi: 10.1016/0092-8674(95)90095-0.
Trypanosoma brucei undergoes antigenic variation in the mammalian host. This can be achieved by activation and inactivation of telomeric variant-specific surface glycoprotein genes (vsg). In procyclic (insect midgut stage) cells, Vsg is not expressed. The mechanisms that regulate transcription of vsg expression sites (ESs) are unknown. Here we demonstrate that transcription from three different promoters was repressed when they were inserted at a transcriptionally silent telomere-proximal locus in bloodstream-form cells. This position effect was stable and heritable. Only transcription from an ES promoter was repressed in procyclic cells. The observed position effect and the promoter-specific developmental regulation suggest that these phenomena reflect the mechanisms that regulate vsg expression.
布氏锥虫在哺乳动物宿主体内会发生抗原变异。这可通过端粒变体特异性表面糖蛋白基因（vsg）的激活和失活来实现。在原循环期（昆虫中肠阶段）细胞中，Vsg不表达。调节vsg表达位点（ESs）转录的机制尚不清楚。在此，我们证明，当三个不同的启动子插入到血流形式细胞中转录沉默的端粒近端位点时，它们的转录受到抑制。这种位置效应是稳定且可遗传的。在原循环期细胞中，只有来自ES启动子的转录受到抑制。观察到的位置效应和启动子特异性发育调控表明，这些现象反映了调节vsg表达的机制。
