Chelm B K, Hoben P J, Hallick R B
Biochemistry. 1977 Feb 22;16(4):782-6. doi: 10.1021/bi00623a033.
The cellular content of chloroplast DNA in Euglena gracilis has been quantitatively determined. DNA was extracted from Euglena cells at various stages of chloroplast development and renatured in the presence of trace amounts of 3H-labeled chloroplast DNA. From the kinetics of renaturation of the 3H-labeled chloroplast DNA, compared with the kinetics of renaturation of excess nonradioactive chloroplast DNA, the fraction of cellular DNA represented by chloroplast DNA was calculated. The content of chloroplast DNA was found to increase from 4.9 to 14.6% of cellular DNA during light-induced chloroplast development. Correcting for the change in DNA mass per cell, the number of copies of chloroplast DNA is found to vary from 1400 to 2900 per cell. During this developmental transition, the cellular content of the chloroplast ribosomal RNA genes varies from 1900 to 5200 copies per cell. The ratio of the number of copies of rRNA genes to chloroplast genomes per cell remains in the range of 1-2 throughout chloroplast development, ruling out selective amplification of chloroplast rRNA genes as a means of regulation of rRNA gene expression. Direct measurement of the number of rRNA cistrons per 9.2 X 10(7) dalton genome yields a value of 1 or 2.
已经对纤细裸藻叶绿体DNA的细胞含量进行了定量测定。从叶绿体发育不同阶段的裸藻细胞中提取DNA，并在痕量3H标记的叶绿体DNA存在下使其复性。根据3H标记的叶绿体DNA的复性动力学，与过量非放射性叶绿体DNA的复性动力学相比较，计算出由叶绿体DNA代表的细胞DNA的比例。发现在光诱导的叶绿体发育过程中，叶绿体DNA的含量从细胞DNA的4.9%增加到14.6%。校正每个细胞中DNA质量的变化后，发现每个细胞中叶绿体DNA的拷贝数在1400至2900之间变化。在这个发育转变过程中，叶绿体核糖体RNA基因的细胞含量从每个细胞1900个拷贝变化到5200个拷贝。在整个叶绿体发育过程中，每个细胞中rRNA基因拷贝数与叶绿体基因组数的比率保持在1至2的范围内，排除了叶绿体rRNA基因的选择性扩增作为rRNA基因表达调控手段的可能性。对每9.2×10(7)道尔顿基因组中rRNA顺反子数量的直接测量得出的值为1或2。
