Biology Department, McMaster University, Hamilton, Ontario L8S4L8, Canada.
Genome Res. 2010 Jun;20(6):755-60. doi: 10.1101/gr.101246.109. Epub 2010 Jan 7.
Low complexity and homopolymer sequences within coding regions are known to evolve rapidly. While their expansion may be deleterious, there is increasing evidence for a functional role associated with these amino acid sequences. Homopolymer sequences are thought to evolve mostly through replication slippage and, therefore, they may be expected to be longer in regions with relaxed selective constraint. Within the coding sequences of eukaryotes, alternatively spliced exons are known to evolve under relaxed constraints in comparison to those exons that are constitutively spliced because they are not included in all of the mature mRNA of a gene. This relaxed exposure to selection leads to faster rates of evolution for alternatively spliced exons in comparison to constitutively spliced exons. Here, we have tested the effect of splicing on the structure (composition, length) of homopolymer sequences in relation to the splicing pattern in which they are found. We observed a significant relationship between alternative splicing and homopolymer sequences with alternatively spliced genes being enriched in number and length of homopolymer sequences. We also observed lower codon diversity and longer homocodons, suggesting a balance between slippage and point mutations linked to the constraints imposed by selection.
低复杂度和同源多聚序列在编码区中被认为进化迅速。虽然它们的扩张可能是有害的，但越来越多的证据表明这些氨基酸序列与功能有关。同源多聚序列被认为主要通过复制滑动进化，因此，在选择压力较弱的区域，它们可能会更长。在真核生物的编码序列中，与组成性剪接的外显子相比，可变剪接的外显子在进化过程中受到的约束较为宽松，因为它们并不包含在基因的所有成熟 mRNA 中。这种对选择的宽松暴露导致可变剪接的外显子比组成性剪接的外显子进化速度更快。在这里，我们研究了剪接对同源多聚序列结构（组成、长度）的影响，以及它们的剪接模式。我们观察到，可变剪接与同源多聚序列之间存在显著的关系，具有可变剪接的基因在同源多聚序列的数量和长度上更为丰富。我们还观察到较低的密码子多样性和更长的同型密码子，这表明滑动和点突变之间存在平衡，与选择施加的限制有关。
