THE TRANSPOSITION UNIT OF VARIANT SURFACE GLYCOPROTEIN GENE-118 OF TRYPANOSOMA-BRUCEI - PRESENCE OF REPEATED ELEMENTS AT ITS BORDER AND ABSENCE OF PROMOTER-ASSOCIATED SEQUENCES
THE TRANSPOSITION UNIT OF VARIANT SURFACE GLYCOPROTEIN GENE-118 OF TRYPANOSOMA-BRUCEI - PRESENCE OF REPEATED ELEMENTS AT ITS BORDER AND ABSENCE OF PROMOTER-ASSOCIATED SEQUENCES
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DOI：
10.1016/s0022-2836(83)80034-5
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发表时间：
1983-01-01
影响因子：
5.6
通讯作者：
BORST, P
中科院分区：
文献类型：
--
作者：
LIU, AYC;VANDERPLOEG, LHT;BORST, P
在 DNA 水平上，锥虫的抗原变异是通过在具有强启动子的表达位点用另一个变异表面糖蛋白 (VSG) 基因替换 1 个变异表面糖蛋白 (VSG) 基因来实现的。在几个研究案例中，VSG 基因的表达动员涉及复制转座。确定了此类 VSG（VSG 118）的大部分转座片段的 DNA 序列。在 3'' 侧，转置片段在基因末端结束；在 5'' 侧，转置片段前面有一个假定的 VSG 基因，扩展了先前的结论，即 VSG 基因紧密聚集。转置段的总长度约为3.5倍。 103 个碱基对和 1.8 倍。其中 103 个碱基对编码 VSG 118 mRNA。在转置片段的 5'' 边界附近，有 5 个约 70 个碱基对的不完美重复，这些重复也存在于其他 VSG 基因的前面，如杂交所示。 3 个次要 VSG 118 特异性转录本的末端位于这些重复序列内。这些重复序列有可能采用非 B-DNA 构象，并且可能在表达位点交换 VSG 基因的重组过程中发挥作用，或者在前 mRNA 加工中发挥作用（不太可能）。之前对 DNA 和 mRNA 序列的比较表明，35 个核苷酸的末端轴突被剪接到 RNA 的主体上。这 35 个核苷酸不在转座片段中，因此它们必须由表达位点贡献。这令人信服地证明转座通过启动子添加而不是位置效应来激活 VSG 基因表达。
At the DNA level, antigenic variation in trypanosomes is brought about by the replacement of 1 variant surface glycoprotein (VSG) gene by another in an expression site with a strong promoter. In several cases studied, mobilization of a VSG gene for expression involves a duplication-transposition. The DNA sequence of most of the transposed segment of one such VSG, the VSG 118, was determined. At the 3'' side, the transposed segment ends within the end of the gene; at the 5'' side, the transposed segment is preceded by a putative VSG gene, extending a previous conclusion that VSG genes are tightly clustered. The total length of the tranposed segment is about 3.5 .times. 103 base-pairs and 1.8 .times. 103 base-pairs of this codes for the VSG 118 mRNA. Near the 5'' border of the transposed segment there are 5 imperfect repeats of about 70 base-pairs that are also present in front of other VSG genes, as shown by hybridization. The termini of 3 minor VSG 118-specific transcripts map within these repeats. The repeats have the potential to adopt non-B-DNA conformations, and could play a role in the recombination process that exchanges VSG genes in the expression site or, less likely, in pre-mRNA processing. Comparison of the DNA and mRNA sequence previously revealed that a terminal axon of 35 nucleotides is spliced onto the main body of the RNA. These 35 nucleotides are not in the transposed segment and they must therefore be contributed by the expression site. This argues persuasively that the transposition activates VSG gene expression by promoter addition rather than by a position effect.