Gockel G, Hachtel W, Baier S, Fliss C, Henke M
Botanisches Institut, Universität Bonn, Germany.
Curr Genet. 1994 Sep;26(3):256-62. doi: 10.1007/BF00309557.
The colourless, nonphotosynthetic protist Astasia longa is phylogenetically related to Euglena gracilis. The 73-kb plastid DNA (ptDNA) of A. longa is about half the size of most chloroplast DNAs (cpDNAs). More than 38 kb of the Astasia ptDNA sequence has been determined. No genes for photosynthetic function have been found except for rbcL. Identified genes include rpoB, tufA, and genes coding for three rRNAs, 17 tRNAs, and 13 ribosomal proteins. Not only is the nucleotide sequence of these genes highly conserved between A. longa and E. gracilis, but a number of these genes are clustered in a similar fashion and have introns in the same positions in both species. The results further support the idea that photosynthetic genes normally encoded in cpDNA have been preferentially lost in Astasia, but that the chloroplast genes coding for components of the plastid translational apparatus have been maintained. This apparatus might be needed for the expression of rbcL and also for that of still unidentified nonphotosynthetic genes of Astasia ptDNA.
无色的非光合原生生物长眼虫在系统发育上与纤细裸藻相关。长眼虫73 kb的质体DNA（ptDNA）大约是大多数叶绿体DNA（cpDNA）大小的一半。长眼虫ptDNA序列已确定超过38 kb。除了rbcL外，未发现光合功能基因。已鉴定的基因包括rpoB、tufA以及编码三种rRNA、17种tRNA和13种核糖体蛋白的基因。这些基因的核苷酸序列不仅在长眼虫和纤细裸藻之间高度保守，而且其中许多基因以相似的方式成簇，并且在两个物种的相同位置具有内含子。结果进一步支持了这样的观点，即通常在cpDNA中编码的光合基因在长眼虫中已被优先丢失，但编码质体翻译装置成分的叶绿体基因得以保留。这种装置可能是rbcL表达以及长眼虫ptDNA中仍未鉴定的非光合基因表达所必需的。
