Mian A, Dover G A
Department of Genetics, University of Cambridge, UK.
Nucleic Acids Res. 1990 Jul 11;18(13):3795-801. doi: 10.1093/nar/18.13.3795.
The sequences of thirty D. melanogaster ribosomal DNA promoter regions have been determined. Fifteen of these were isolated from a wild population recently captured in North Wootten, England. The other fifteen were isolated from an inbred laboratory strain. The overall level of variation is almost twice as high in the North Wootten strain as in the inbred laboratory strain. Two mutations at nucleotides -17 and -21 relative to transcription start, fall directly within a region known to be transcriptionally important. The sequences are also compared to eight previously published sequences from another D. melanogaster strain, Oregon R. Two of these eight clones have a -17 mutation identical to the one found in this study, suggesting that this polymorphism is widespread. Strikingly, all eight of these clones carry two single base pair changes not found in any of the other thirty clones, indicating the extent with which promoter variants can be homogenized and fixed in a population. Polymorphisms show different levels of homogenization within the rDNA unit spacer repeats or between different arrays depending on the location of the polymorphism. This has implications for the evolution of the observed species-specific transcription of ribosomal RNA genes.
已确定了三十个黑腹果蝇核糖体DNA启动子区域的序列。其中十五个是从最近在英国北伍滕捕获的野生种群中分离出来的。另外十五个是从一个近交实验室品系中分离出来的。北伍滕品系的总体变异水平几乎是近交实验室品系的两倍。相对于转录起始点，在核苷酸-17和-21处的两个突变直接位于一个已知具有转录重要性的区域内。这些序列还与之前发表的来自另一个黑腹果蝇品系俄勒冈R的八个序列进行了比较。这八个克隆中有两个具有与本研究中发现的相同的-17突变，表明这种多态性很普遍。引人注目的是，这八个克隆中的所有克隆都携带两个单碱基对变化，而在其他三十个克隆中均未发现，这表明启动子变体在种群中可以被同质化和固定的程度。根据多态性的位置，多态性在核糖体DNA单位间隔重复序列内或不同阵列之间表现出不同程度的同质化。这对观察到的核糖体RNA基因物种特异性转录的进化具有影响。
