Vigetti Davide, Binelli Giorgio, Monetti Claudio, Prati Mariangela, Bernardini Giovanni, Gornati Rosalba
Dipartimento di Biologia Strutturale e Funzionale, Università degli Studi dell'Insubria, Via J.H. Dunant 3, 21100 Varese, Italy.
J Mol Evol. 2003 Dec;57(6):650-8. doi: 10.1007/s00239-003-2515-5.
During vertebrate evolution, the uric acid degradation pathway has been modified and several enzymes have been lost. Consequently, the end product of purine catabolism varies from species to species. In the past few years, we have focused our attention on vertebrate allantoicase (an uricolytic pathway enzyme), whose activity is present in certain fish and amphibians only, but whose mRNA we detected also in mammals. As allantoicase activity disappeared in amniotes, we wonder why these sequences not only remain present in the mammalian genome, but are still transcribed. To elucidate this issue, we have cloned and analyzed comparable cDNA sequences of different organisms from ascidians to mammals. The analysis of the nonsynonymous-synonymous substitution rate that we performed on the coding region comprising exons 3 to 8 by means of maximum likelihood suggested that a certain amount of purifying selection is acting on the allantoicase sequences. Some implications of the preservation of an apparently unnecessary gene in higher vertebrates are discussed.
在脊椎动物进化过程中，尿酸降解途径发生了改变，几种酶已经丢失。因此，嘌呤分解代谢的终产物因物种而异。在过去几年里，我们将注意力集中在脊椎动物尿囊素酶（一种尿酸分解途径的酶）上，其活性仅在某些鱼类和两栖动物中存在，但我们在哺乳动物中也检测到了其mRNA。由于尿囊素酶活性在羊膜动物中消失，我们不禁要问，为什么这些序列不仅在哺乳动物基因组中仍然存在，而且仍在转录。为了阐明这个问题，我们克隆并分析了从海鞘到哺乳动物等不同生物体的可比cDNA序列。我们通过最大似然法对包含外显子3至8的编码区进行的非同义-同义替换率分析表明，一定量的纯化选择作用于尿囊素酶序列。本文讨论了在高等脊椎动物中保留一个明显不必要的基因的一些影响。
