Roth C, Bringaud F, Layden R E, Baltz T, Eisen H
Unit of Immunoparasitology, Institut Pasteur, Paris, France.
Proc Natl Acad Sci U S A. 1989 Dec;86(23):9375-9. doi: 10.1073/pnas.86.23.9375.
The expression of genes coding for variable surface glycoproteins (VSGs) in Trypanosoma equiperdum is linked to duplicative transpositions of silent, basic copy sequences into telomere-linked expression sites. Examination of three independently derived late-appearing trypanosome clones expressing VSG-78 revealed that the expressed gene in all cases is composed of sequences derived from three or four individual silent genes. The 182 base pairs at the 3' end of the coding sequence are derived from one silent gene, the 3' donor. The remaining 5' segment is a mosaic structure containing variable-length segments derived from two, or perhaps three, related silent genes. All of the silent genes that participate in the construction of the VSG-78 expression-linked copy (ELC) genes contain multiple stop codons and are unable to code for VSGs. Individual silent pseudogenes complement one another in the mosaic structure of the 5' portions of the ELC genes and create functional VSG genes. The joining of the 3' and 5' portions of the composite genes occurs in short regions of homology and suggests a mechanism by which the ordered expression of the VSG genes is generated.
马媾疫锥虫中编码可变表面糖蛋白（VSG）的基因表达与沉默的基本拷贝序列向端粒连接的表达位点的重复转座有关。对三个独立获得的表达VSG-78的晚期出现的锥虫克隆进行检查发现，在所有情况下，表达的基因均由来自三或四个单独沉默基因的序列组成。编码序列3'端的182个碱基对来自一个沉默基因，即3'供体。其余的5'片段是一种镶嵌结构，包含来自两个或可能三个相关沉默基因的可变长度片段。所有参与构建VSG-78表达连接拷贝（ELC）基因的沉默基因都包含多个终止密码子，无法编码VSG。单个沉默假基因在ELC基因5'部分的镶嵌结构中相互补充，从而产生功能性VSG基因。复合基因3'和5'部分的连接发生在短的同源区域，提示了一种产生VSG基因有序表达的机制。
