Crozatier M, Van der Ploeg L H, Johnson P J, Gommers-Ampt J, Borst P
Division of Molecular Biology, The Netherlands Cancer Institute, Amsterdam.
Mol Biochem Parasitol. 1990 Aug;42(1):1-12. doi: 10.1016/0166-6851(90)90107-w.
We have studied the organization of the expression site, in which most chromosome-internal variant-specific surface glycoprotein (VSG) genes of Trypanosoma brucei strain 427 are expressed (the dominant expression site) and compared it to the previously characterized VSG 221 expression site. With the exception of a 500 bp segment and a VSG pseudogene, which are absent from the dominant expression site, overall all major sequence elements of the two sites are organized similarly, as judged from their relative mapping positions by UV inactivation of transcription. Transcription is insensitive to 1 mg alpha-amanitin per ml, a characteristic property of VSG gene expression sites analyzed thus far. The sequence elements of the dominant expression site include at least one other expressed gene of unknown function and homologues of at least two other open reading frames. The large internal duplication of the 60-kb 221 expression site appear to be missing from the dominant site, resulting in a shorter, 40-kb transcription unit. As judged from its relative sensitivity to UV inactivation of transcription, a subsidiary promoter, identified by other methods in the dominant expression site appears fully dependent for its activity on the promoter located 40 kb upstream of the VSG gene. We conclude that all VSG gene expression sites may be similarly organized as large polygenic transcription units.
我们研究了布氏锥虫427株中大多数染色体内部变体特异性表面糖蛋白（VSG）基因在此表达的表达位点（主要表达位点）的组织情况，并将其与先前表征的VSG 221表达位点进行了比较。除了主要表达位点中不存在的一个500 bp片段和一个VSG假基因外，从通过转录的紫外线灭活确定的相对定位位置判断，这两个位点的所有主要序列元件的组织方式相似。转录对每毫升1毫克α-鹅膏蕈碱不敏感，这是迄今为止分析的VSG基因表达位点的一个特征。主要表达位点的序列元件包括至少一个功能未知的其他表达基因以及至少两个其他开放阅读框的同源物。60 kb的221表达位点的大片段内部重复在主要位点似乎缺失，导致转录单元更短，为40 kb。从其对转录紫外线灭活的相对敏感性判断，在主要表达位点通过其他方法鉴定的一个辅助启动子，其活性似乎完全依赖于位于VSG基因上游40 kb处的启动子。我们得出结论，所有VSG基因表达位点可能都类似地组织成大型多基因转录单元。
