Kooter J M, van der Spek H J, Wagter R, d'Oliveira C E, van der Hoeven F, Johnson P J, Borst P
Division of Molecular Biology, Netherlands Cancer Institute, Antoni van Leeuwenhoekhuis, Amsterdam.
Cell. 1987 Oct 23;51(2):261-72. doi: 10.1016/0092-8674(87)90153-x.
The variant specific surface glycoprotein (VSG) genes of T. brucei are expressed in telomeric expression sites. We have determined the structure of the active site in trypanosome variant 221a, which contains VSG gene 221, by analysis of cloned DNA segments that represent 65 kb of the 5'-flanking region of the VSG gene. In nuclear run-on experiments, 57 kb of adjacent sequences are cotranscribed with the VSG gene at approximately similar rates and in the alpha-amanitin-resistant manner characteristic of VSG genes. Besides the VSG mRNA, this expression site yields at least seven stable RNAs, suggesting that it is a multicistronic transcription unit. Our results also show that insertion of a transcriptional terminator is not the general mechanism of switching off expression sites.
布氏锥虫的变异特异性表面糖蛋白（VSG）基因在端粒表达位点表达。我们通过分析代表VSG基因5'侧翼区域65 kb的克隆DNA片段，确定了含有VSG基因221的锥虫变体221a中活性位点的结构。在细胞核连续转录实验中，57 kb的相邻序列与VSG基因以大致相似的速率并以VSG基因特有的α-鹅膏蕈碱抗性方式共转录。除了VSG mRNA外，该表达位点还产生至少七种稳定的RNA，这表明它是一个多顺反子转录单元。我们的结果还表明，插入转录终止子不是关闭表达位点的一般机制。
