Genske J E, Cairns B R, Stack S P, Landfear S M
Department of Microbiology and Immunology, Oregon Health Sciences University, Portland 97201.
Mol Cell Biol. 1991 Jan;11(1):240-9. doi: 10.1128/mcb.11.1.240-249.1991.
We have studied the structure and expression of histone H2B mRNA and genes in the parasitic protozoan Leishmania enrietti. A genomic clone containing three tandemly repeated genes has been sequenced and shown to encode three identical histone proteins and two types of closely related mRNA sequence. We have also sequenced three independent cDNA clones and demonstrated that the Leishmania H2B mRNAs are polyadenylated, similar to the basal histone mRNAs of higher eucaryotes and the histone mRNAs of yeast. In addition, the Leishmania mRNAs contain inverted repeats near the poly(A) tail which could form stem-loops similar in secondary structure, but not in sequence, to the 3' stem-loops of nonpolyadenylated replication-dependent histones of higher eucaryotes. Unlike the replication-dependent histones, the Leishmania histone H2B mRNAs do not decrease in abundance following treatment with inhibitors of DNA synthesis. The histone mRNAs are differentially expressed during the parasite life cycle and accumulate to a higher level in the extracellular promastigotes (the form which in nature lives within the gut of the insect vector) than in the intracellular amastigotes (the form that lives within the mammalian host macrophages).
我们研究了寄生原生动物恩氏利什曼原虫中组蛋白H2B mRNA和基因的结构与表达。一个包含三个串联重复基因的基因组克隆已被测序，结果显示其编码三种相同的组蛋白和两种密切相关的mRNA序列。我们还对三个独立的cDNA克隆进行了测序，并证明利什曼原虫的H2B mRNA是多聚腺苷酸化的，这与高等真核生物的基础组蛋白mRNA以及酵母的组蛋白mRNA相似。此外，利什曼原虫的mRNA在多聚（A）尾附近含有反向重复序列，这些序列可以形成茎环结构，其二级结构与高等真核生物非多聚腺苷酸化的复制依赖性组蛋白的3'茎环相似，但序列不同。与复制依赖性组蛋白不同，用DNA合成抑制剂处理后，利什曼原虫组蛋白H2B mRNA的丰度不会降低。组蛋白mRNA在寄生虫生命周期中差异表达，在细胞外前鞭毛体（在自然界中生活在昆虫媒介肠道内的形态）中积累的水平高于细胞内无鞭毛体（生活在哺乳动物宿主巨噬细胞内的形态）。
