Schreiner M, Geisert M, Oed M, Arendes J, Güngerich U, Breter H J, Stüber K, Weinblum D
Institut für Physiologische Chemie und Pathobiochemie, Johannes Gutenberg-Universität, Mainz, Germany.
J Mol Evol. 1995 Apr;40(4):428-42. doi: 10.1007/BF00164029.
The marine green coccoidal alga Nanochlorum eukaryotum (N.e.) is of small size with an average diameter of 1.5 microns. It is characterized by primitive-appearing biochemical and morphological properties, which are considerably different from those of other green algae. Thus, it has been proposed that N.e. may be an early developed algal form. To prove this hypothesis, DNA of N.e. was isolated by a phenol extraction procedure, and the chloroplast DNA separated by preparative CsCl density-gradient centrifugation. The kinetic complexity of the nuclear and of the chloroplast DNA was evaluated by reassociation kinetics to 3 x 10(7) bp and 9 x 10(4) bp, respectively. Several chloroplast genes, including the rRNA genes, were cloned on distinct fragments. The order of the rRNA genes corresponds to the common prokaryotic pattern. The 16S rRNA gene comprises 1,548 bases and is separated from the 23S rRNA gene with its 2,920 bases by a short spacer of 460 bases, which also includes the tRNA(Ile) and tRNA(Ala) genes. The 5S rRNA gene has not been found; it must start further than 500 bases downstream from the 3'-end of the 23S rRNA gene. From the chloroplast rRNA sequences, we have deduced secondary structures of the 16S and 23S rRNAs, which are in agreement with standard models. The rRNA sequences were aligned with corresponding chloroplast sequences; phylogenetic relationships were calculated by several methods. From these calculations, we conclude that N.e. is most closely related to Chlorella vulgaris. Therefore, N.e. does not represent an early developed algal species; the primitive-appearing morphological and biochemical characteristics of N.e. must rather be explained by secondary losses.
海洋绿球藻Nanochlorum eukaryotum（N.e.）体积小，平均直径为1.5微米。其特点是具有看似原始的生化和形态学特性，与其他绿藻有很大不同。因此，有人提出N.e.可能是一种早期发育的藻类形式。为了验证这一假设，通过酚提取法分离了N.e.的DNA，并通过制备性CsCl密度梯度离心法分离了叶绿体DNA。通过复性动力学评估核DNA和叶绿体DNA的动力学复杂度，分别为3×10⁷bp和9×10⁴bp。包括rRNA基因在内的几个叶绿体基因被克隆到不同的片段上。rRNA基因的顺序与常见的原核模式相对应。16S rRNA基因包含1548个碱基，与含有2920个碱基的23S rRNA基因被一个460个碱基的短间隔区隔开，该间隔区还包括tRNA（Ile）和tRNA（Ala）基因。未发现5S rRNA基因；它一定位于23S rRNA基因3'端下游500多个碱基处。从叶绿体rRNA序列中，我们推导了16S和23S rRNA的二级结构，这些结构与标准模型一致。将rRNA序列与相应的叶绿体序列进行比对；通过几种方法计算系统发育关系。从这些计算中，我们得出结论，N.e.与普通小球藻关系最为密切。因此，N.e.并不代表一种早期发育的藻类物种；N.e.看似原始的形态和生化特征更应该用次生损失来解释。
