Selective pressure on the allantoicase gene during vertebrate evolution.
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.
Vigetti
Davide
D
Dipartimento di Biologia Strutturale e Funzionale, Università degli Studi dell'Insubria, Via J.H. Dunant 3, 21100 Varese, Italy.
Binelli
Giorgio
G
Monetti
Claudio
C
Prati
Mariangela
M
Bernardini
Giovanni
G
Gornati
Rosalba
R
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D012641:Selection, Genetic; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014512:Ureohydrolases / Q000235:genetics*; D014714:Vertebrates / Q000235:genetics*
D018076:DNA, Complementary; D014512:Ureohydrolases; C019658:allantoicase