Chloroplast protein and centrosomal genes, a tRNA intron, and odd telomeres in an unusually compact eukaryotic genome, the cryptomonad nucleomorph.
Chloroplast protein and centrosomal genes, a tRNA intron, and odd telomeres in an unusually compact eukaryotic genome, the cryptomonad nucleomorph.
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叶绿体蛋白和中心体基因、tRNA 内含子和异常紧凑的真核基因组（隐单胞菌核形态）中的奇怪端粒。
DOI：
10.1073/pnas.97.1.200
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发表时间：
2000
影响因子：
11.1
通讯作者：
S. Douglas
中科院分区：
文献类型：
--
作者：
S. Zauner;M. Fraunholz;J. Wastl;S. Penny;M. Beaton;T. Cavalier;U. Maier;S. Douglas
几个主要藻类的细胞是两种完全不同的真核细胞的进化嵌合体。大多数这些“细胞内的细胞”失去了以前藻类内共生体的细胞核。但数亿年后，隐单胞菌仍然保留着它们以前的红藻内共生体的细胞核，作为一种微小的残余细胞器，即核形态，它具有三条微小的线性染色体，但它们的功能和末端的性质尚不清楚。我们报告了来自 Guillardia theta 三个染色体每一个末端的大量隐单胞菌核形序列 (68.5 kb)。核型染色体的端粒与其他真核生物的端粒显着不同，是 23 聚体序列 (AG)(7)AAG(6)A 的重复，而不是典型的六聚体（通常为 TTAGGG）。包含 rRNA 顺反子和一个蛋白质编码基因的亚末端区域在所有三个染色体末端精确重复。基因密度（每 0.8 kb 一个）是所有细胞基因组中最高的。 38 个蛋白质编码基因均不具有剪接体内含子，这与绿蛛植物核形态形成鲜明对比。大多数已鉴定的核型基因用于基因表达或蛋白质降解；组蛋白、微管蛋白和假定的中心体 ranbpm 基因可能对染色体分离很重要。尚未发现初级或次级代谢的基因。三个 tRNA 基因中的两个具有内含子，其中一个位于迄今未被描述的位置。基因间区域特别短；由两种不同的RNA聚合酶转录的三个基因与它们的邻居重叠。报道的序列编码两种必需的叶绿体蛋白：FtsZ 和红氧还蛋白，从而解释了隐单胞菌核型持续存在的原因。
Cells of several major algal groups are evolutionary chimeras of two radically different eukaryotic cells. Most of these "cells within cells" lost the nucleus of the former algal endosymbiont. But after hundreds of millions of years cryptomonads still retain the nucleus of their former red algal endosymbiont as a tiny relict organelle, the nucleomorph, which has three minute linear chromosomes, but their function and the nature of their ends have been unclear. We report extensive cryptomonad nucleomorph sequences (68.5 kb), from one end of each of the three chromosomes of Guillardia theta. Telomeres of the nucleomorph chromosomes differ dramatically from those of other eukaryotes, being repeats of the 23-mer sequence (AG)(7)AAG(6)A, not a typical hexamer (commonly TTAGGG). The subterminal regions comprising the rRNA cistrons and one protein-coding gene are exactly repeated at all three chromosome ends. Gene density (one per 0.8 kb) is the highest for any cellular genome. None of the 38 protein-coding genes has spliceosomal introns, in marked contrast to the chlorarachniophyte nucleomorph. Most identified nucleomorph genes are for gene expression or protein degradation; histone, tubulin, and putatively centrosomal ranbpm genes are probably important for chromosome segregation. No genes for primary or secondary metabolism have been found. Two of the three tRNA genes have introns, one in a hitherto undescribed location. Intergenic regions are exceptionally short; three genes transcribed by two different RNA polymerases overlap their neighbors. The reported sequences encode two essential chloroplast proteins, FtsZ and rubredoxin, thus explaining why cryptomonad nucleomorphs persist.