Bernardi G, Hughes S, Mouchiroud D
Laboratoire de Genetique Moleculaire, Institut Jacques Monod, Paris, France.
J Mol Evol. 1997;44 Suppl 1:S44-51. doi: 10.1007/pl00000051.
The vertebrate genome underwent two major compositional transitions, between therapsids and mammals and between dinosaurs and birds. These transitions concerned a sizable part (roughly one-third) of the genome, the gene-richest part of it, and consisted in an increase in GC levels (GC is the molar fraction of guanine + cytosine in DNA) which affected both coding sequences (especially third codon positions) and noncoding sequences. These major transitions were studied here by comparing GC3 levels (GC3 is the GC of third codon positions) of orthologous genes from Xenopus, chicken, calf, and man.
脊椎动物基因组经历了两次主要的组成转变，一次发生在兽孔目爬行动物和哺乳动物之间，另一次发生在恐龙和鸟类之间。这些转变涉及基因组中相当大的一部分（约三分之一），即基因最丰富的部分，其表现为GC含量（GC是DNA中鸟嘌呤 + 胞嘧啶的摩尔分数）的增加，这一增加同时影响了编码序列（特别是第三密码子位置）和非编码序列。本文通过比较非洲爪蟾、鸡、小牛和人类直系同源基因的GC3含量（GC3是第三密码子位置的GC）对这些主要转变进行了研究。
