Division of Cell and Molecular Biology, Sir Alexander Fleming Building, Imperial College London, South Kensington, London SW7 2AZ, UK.
Nucleic Acids Res. 2011 Mar;39(6):2018-31. doi: 10.1093/nar/gkq950. Epub 2010 Nov 13.
Trypanosoma brucei mono-allelically expresses one of approximately 1500 variant surface glycoprotein (VSG) genes while multiplying in the mammalian bloodstream. The active VSG is transcribed by RNA polymerase I in one of approximately 15 telomeric VSG expression sites (ESs). T. brucei is unusual in controlling gene expression predominantly post-transcriptionally, and how ESs are mono-allelically controlled remains a mystery. Here we identify a novel transcription regulator, which resembles a nucleoplasmin-like protein (NLP) with an AT-hook motif. NLP is key for ES control in bloodstream form T. brucei, as NLP knockdown results in 45- to 65-fold derepression of the silent VSG221 ES. NLP is also involved in repression of transcription in the inactive VSG Basic Copy arrays, minichromosomes and procyclin loci. NLP is shown to be enriched on the 177- and 50-bp simple sequence repeats, the non-transcribed regions around rDNA and procyclin, and both active and silent ESs. Blocking NLP synthesis leads to downregulation of the active ES, indicating that NLP plays a role in regulating appropriate levels of transcription of ESs in both their active and silent state. Discovery of the unusual transcription regulator NLP provides new insight into the factors that are critical for ES control.
在哺乳动物血液中繁殖时，布氏锥虫单等位基因表达大约 1500 个变体表面糖蛋白 (VSG) 基因中的一个。活性 VSG 由 RNA 聚合酶 I 在大约 15 个端粒 VSG 表达位点 (ES) 中的一个转录。布氏锥虫在转录后主要控制基因表达是不寻常的，ES 如何单等位基因控制仍然是一个谜。在这里，我们鉴定了一种新型转录调节剂，它类似于具有 AT 钩基序的核质蛋白样蛋白 (NLP)。NLP 是血液形式的 T. brucei ES 控制的关键，因为 NLP 敲低导致沉默的 VSG221 ES 的去抑制达到 45-65 倍。NLP 还参与抑制非活性 VSG Basic Copy 阵列、微染色体和前环素基因座的转录。结果表明，NLP 富集在 177 和 50bp 简单重复序列、rDNA 和前环素周围的非转录区以及活性和沉默 ES 上。阻断 NLP 合成导致活性 ES 的下调，表明 NLP 在调节 ES 在其活性和沉默状态下的适当转录水平方面发挥作用。新型转录调节剂 NLP 的发现为 ES 控制的关键因素提供了新的见解。
