16s rRNA的保守字和进化树重建(英文)

Conserved Words in 16s Ribosomal RNA Deduced from Evolutionary Tree Reconstruction

据寡核苷 ( n核苷 )频数差定义进化距离 ,由此构成 1 6 s r RNA进化树 ,当 n=7,8时和实验资料符合很好 ,在寻找出全部进化相关的 7-核苷的基础上 ,本文进一步求得了长度大于 7的保守字 ,它们在一个界别中的诸物种中高度保守 ,并出现于核糖体序列的基本相同的位置上 。

Evolutionary distance is defined by oligonucleotide ( n -bases) frequency difference of two sequences.Phylogenetic tree is reconstructed using a set of 16S (18S) rRNA sequences and the definition of distance.The quality of trees generally improves with increasing n and reaches a plateau of best fit at n =7 or 8.So,the 7-mer or 8-mer frequencies provides a basis to describe rRNA evolution.Then,a group of 7-mers are deduced which are correlate well with evolution.Evolution-related conservative words longer than 7 bases for Bacteria and Archaea in 16S rRNA sequences have been found.They are highly conserved in nearly all species of a kingdom (or a sub-kingdom) and are located on nearly same sites of sequences. The structural meaning of these conservative words is discussed briefly.