长苞铁杉nrDNA内转录间隔区及5.8S的二级结构分析研究

核糖体RNA及相邻区域的二级结构研究,作为一个重要的工具,已在一些分类等级上被应用于系统发育的分析。以长苞铁杉为实验材料,通过克隆、测序,利用最小自由能原理预测nrDNA内转录间隔区及5.8S转录本的二级结构,分析它们的结构特点,探讨假基因化拷贝与功能拷贝结构上的差异。分析结果表明:(1)ITS1区的二级结构主要由几个延展的发夹结构组成,配对的亚重复单位在松科植物特有的保守序列处有部分重叠,未配对的亚重复单位通常能自身折叠,保守序列的部分碱基出现在发夹结构的环中;(2)假基因化拷贝二级结构的自由能比正常拷贝高;(3)与正常拷贝的二级结构相比,假基因化拷贝在进化速率很低的5.8S功能区发生较大的变异,且在5.8 S末端没有和26 S连接配对。

Secondary Structure Analysis on the nrDNA Internal Transcribed Spacers and 5.8 S in Nothotsuga longibracteata

Studies on the secondary structures of rRNAs and adjacent regions has been considered as an important tool for inferring phylogenetic relationships at some taxonomic levels.Based on molecular clone,sequencing and secondary structure analysis on nrDNA ITS and 5.8 S region in Nothotsuga longibracteata by the principle of minimizing free energy,structural characteristics were studied.Moreover,we discussed the structural differences between pseudogenic copy and functional copies.The results showed as follows:(1) the secondary structure of ITS1 is dominated by several extended haipins,with paired subrepeats partially overlapping at the conserved motif unique for Pinaceae,while unpaired subrepeats being fold onto itself and leaving part of the conserved motif exposed in hairpin loops;(2) the free energy value of pseudogenic copy is often higher than that of functional copy;(3)compared with functional copies,the pseudogenic copy has more variable sites in the 5.8 S region,which is symbolized by slow evolution rate,and has no contact sites in the 3' end with 26 S ribosomal RNA.