Slightom J L, Chang L Y, Koop B F, Goodman M
Department of Genetics, University of Wisconsin-Madison.
Mol Biol Evol. 1985 Sep;2(5):370-89. doi: 10.1093/oxfordjournals.molbev.a040357.
The fetal globin genes G gamma and A gamma from one chromosome of a chimpanzee (Pan troglodytes) were sequenced and found to be closely similar to the corresponding genes of man and the gorilla. These genes contain identical promoter and termination signals and have exons 1 and 2 separated by the conserved short intron 1 (122 bp) and exons 2 and 3 separated by the more rapidly evolving, larger intron 2 (893 bp and 887 bp in chimpanzee G gamma and A gamma, respectively). Each intron 2 has a stretch of simple sequence DNA (TG)n serving possibly as a "hot spot" for recombination. The two chimpanzee genes encode polypeptide chains that differ only at position 136 (glycine in G gamma and alanine in A gamma) and that are identical to the corresponding human chains, which have aspartic acid at position 73 and lysine at 104 in contrast to glycine and arginine at these respective positions of the gorilla A gamma chain. Phylogenetic analysis by the parsimony method revealed four silent (synonymous) base substitutions in evolutionary descent of the chimpanzee G gamma and A gamma codons and none in the human and gorilla codons. These Homininae (Pan, Homo, Gorilla) coding sequences evolved at one-tenth the average mammalian rate for nonsynonymous and one-fourth that for synonymous substitutions. Three sequence regions that were affected by gene conversions between chimpanzee G gamma and A gamma loci were identified: one extended 3' of the hot spot with G gamma replaced by the A gamma sequence, another extended 5' of the hot spot with A gamma replaced by G gamma, and the third conversion extended from the 5' flanking to the 5' end of intron 2, with G gamma replaced here by the A gamma sequence. A conversion similar to this third one has occurred independently in the descent of the gorilla genes. The four previously identified conversions, labeled C1-C4 (Scott et al. 1984), were substantiated with the addition of the chimpanzee genes to our analysis (C1 being shared by all three hominines and C2, C3, and C4 being found only in humans). Thus, the fetal genes from all three of these hominine species have been active in gene conversions during the descent of each species.
对一只黑猩猩（黑猩猩属）一条染色体上的胎儿珠蛋白基因Gγ和Aγ进行了测序，发现它们与人类和大猩猩的相应基因非常相似。这些基因含有相同的启动子和终止信号，外显子1和2被保守的短内含子1（122 bp）隔开，外显子2和3被进化较快、较大的内含子2隔开（黑猩猩Gγ和Aγ中的内含子2分别为893 bp和887 bp）。每个内含子2都有一段简单序列DNA（TG）n，可能作为重组的“热点”。这两个黑猩猩基因编码的多肽链仅在第136位不同（Gγ中为甘氨酸，Aγ中为丙氨酸），并且与相应的人类链相同，人类链在第73位为天冬氨酸，在第104位为赖氨酸，而大猩猩Aγ链在这些相应位置为甘氨酸和精氨酸。通过简约法进行的系统发育分析显示，在黑猩猩Gγ和Aγ密码子的进化谱系中有四个沉默（同义）碱基替换，而人类和大猩猩密码子中没有。这些人亚科（黑猩猩属、人属、大猩猩属）的编码序列在非同义替换方面的进化速度是哺乳动物平均速度的十分之一，在同义替换方面是四分之一。确定了三个受黑猩猩Gγ和Aγ基因座之间基因转换影响的序列区域：一个在热点的3'端延伸，Gγ被Aγ序列取代；另一个在热点的5'端延伸，Aγ被Gγ取代；第三个转换从5'侧翼延伸到内含子2的5'端，这里Gγ被Aγ序列取代。在大猩猩基因的谱系中独立发生了一次与第三次类似的转换。在我们的分析中加入黑猩猩基因后，证实了之前确定的四个转换，标记为C1 - C4（斯科特等人，1984年）（C1为所有三个人亚科共有，C2、C3和C4仅在人类中发现）。因此，在每个物种的谱系中，这三个物种的胎儿基因都参与了基因转换。
