逆转座子与生物遗传多样性

Retroposon and Genetic Diversity

生物为了适应环境变化 ,需要遗传物质发生变化来为进化提供材料 ,在进化过程中遗传物质的变化方式主要包括突变和基因重排。对一个种群或个体来讲 ,在不同的环境或一定生活周期内的不同阶段 ,基因组存在着基因的差次表达 ,这种调控在核酸分子水平上主要是通过突变和基因重排来实现 ,由此使得基因组成为一个动态变化的体系 ,使种群或个体的遗传多样性发生相应的变化。分子生物学中最惊人的发现之一是在基因组内存在着通过DNA转录为RNA后 ,再经逆转录成为cDNA并插入到基因组的新位点上的因子 ,被称为逆转座子。按照其结构特点以及所编码反转录蛋白因子的不同 ,可分为反转录转位因子 ,反转录子 ,反转录病毒 ,能编码反转录所需蛋白的因子 ,不能编码反转录所需蛋白的因子。逆转座子在转位过程中须以RNA作为中间体 ,RNA较易变异 ,且RNA聚合酶和逆转录酶均无校对功能 ,这就使得逆转座子具有高度变异性。逆转座子可通过遗传变异、基因重排或对基因表达的影响 ,导致生物遗传多样性的形成。逆转座子除了能够促进基因的流动性增加遗传多样性外 ,它们散布在基因组中 ,还能够成为进化的种子。

In order to adapt to changing environments all species need variation in genetic material. This variation is mainly created by two processes—mutation and gene rearrangement. With respect to a population or an individual inside a population, there is differential expression of genes in genome in different environments or various phases of a specific life cycle. This kind of gene regulation is achieved by mutation and gene rearrangement at the nucleotide level. The genome is a dynamic system, and the genetic diversity of the population or individual is changing accordingly. Retroposons are one of the most surprising elements in molecular biology. Retroposons use RNA as their midbody, transcript DNA to RNA, and reverse transcript RNA to cDNA, finally inserting this cDNA into a new part of the genome. Because of this transposition function they can be considered a transposable element. According to the character of their structure and the different reverse transcription protein factors they code for, they have been classed as reverse transposition elements; retrotransposons, retroviruses, retroposons which can code reverse transcriptase and those which can not code reverse transcriptase. Retroposons need RNA as a midbody to complete transposition. However, RNA is apt to change, and RNA polymerase and reverse transcriptase lack an error correction function. For these reasons, retroposons have high genetic variability. Retroposons can increase the genetic diversity of living beings by causing hereditary variation, directly rearranging genes, or by affecting gene expression. Besides the functions of accelerating gene flux and increasing genetic diversity, retroposons scattered within the genome could be the very source of the variation required for adaptation and evolution.