Jermiin L S, Crozier R H
Department of Genetics and Human Variation, La Trobe University, Bundoora, Victoria, Australia.
J Mol Evol. 1994 Mar;38(3):282-94. doi: 10.1007/BF00176090.
Polymerase chain reaction (PCR) followed by sequencing of single-stranded DNA yielded sequence information from the cytochrome b (cyt b) region in mitochondrial DNA from the ant Tetraponera rufoniger. Compared with the cyt b genes from Apis mellifera, Drosophila melanogaster, and D. yakuba, the overall A+T content (A+T%) of that of T. rufoniger is lower (69.9% vs 80.7%, 74.2%, and 73.9%, respectively) than those of the other three. The codon usage in the cyt b gene of T. rufoniger is biased although not as much as in A. mellifera, D. melanogaster, and D. yakuba; T. rufoniger has eight unused codons whereas D. melanogaster, D. yakuba, and A. mellifera have 21, 20, and 23, respectively. The inferred cyt b polypeptide chain (PPC) of T. rufoniger has diverged at least as much from a common ancestor with D. yakuba as has that of A. mellifera (approximately 3.5 vs approximately 2.9). Despite the lower A+T%, the relative frequencies of amino acids in the cyt b PPC of T. rufoniger are significantly (P < 0.05) associated with the content of adenine and thymine (A+T%) and size of codon families. The mitochondrially located cytochrome oxidase subunit II genes (CO-II) of endopterygote insects have significantly higher average A+T% (approximately 75%) than those of exopterygous (approximately 69%) and paleopterous (approximately 69%) insects. The increase in A+T% of endopterygote insects occurred in Upper Carboniferous and coincided with a significant acceleration of PPC divergence. However, acceleration of PPC divergence is not significantly correlated with the increase of the A+T% (P > 0.1). The high A+T%, the biased codon usage, and the increased PPC divergence of Hymenoptera can in that respect most easily be explained by directional mutation pressure which began in the Upper Carboniferous and still occurs in most members of the order. Given the roughly identical A+T% of the cyt b and CO-II genes from the other insects whose DNA sequences are known (A. mellifera, D. melanogaster, and D. yakuba), it seems most likely that the A+T% of T. rufoniger declined secondarily within the last 100 Myr as a result of a reduced directional mutation pressure.
通过聚合酶链反应（PCR）对单链DNA进行测序，得到了红褐举腹蚁线粒体DNA细胞色素b（cyt b）区域的序列信息。与意大利蜜蜂、黑腹果蝇和雅库布果蝇的cyt b基因相比，红褐举腹蚁的总体A+T含量（A+T%）较低（分别为69.9%，而其他三种果蝇分别为80.7%、74.2%和73.9%）。红褐举腹蚁cyt b基因的密码子使用存在偏向性，尽管不如意大利蜜蜂、黑腹果蝇和雅库布果蝇明显；红褐举腹蚁有8个未使用的密码子，而黑腹果蝇、雅库布果蝇和意大利蜜蜂分别有21个、20个和23个。推断出的红褐举腹蚁细胞色素b多肽链（PPC）与雅库布果蝇共同祖先的差异程度至少与意大利蜜蜂的相同（约3.5与约2.9）。尽管A+T%较低，但红褐举腹蚁cyt b PPC中氨基酸的相对频率与腺嘌呤和胸腺嘧啶含量（A+T%）以及密码子家族大小显著相关（P < 0.05）。内翅类昆虫线粒体中的细胞色素氧化酶亚基II基因（CO-II）的平均A+T%（约75%）显著高于外翅类昆虫（约69%）和古翅类昆虫（约69%）。内翅类昆虫A+T%的增加发生在上石炭统，与PPC分歧的显著加速同时出现。然而，PPC分歧的加速与A+T%增加没有显著相关性（P > 0.1）。膜翅目昆虫高A+T%、偏向的密码子使用和增加的PPC分歧在这方面最容易用始于上石炭统且仍存在于该目大多数成员中的定向突变压力来解释。鉴于已知DNA序列的其他昆虫（意大利蜜蜂、黑腹果蝇和雅库布果蝇）的cyt b和CO-II基因的A+T%大致相同，红褐举腹蚁的A+T%很可能在过去1亿年内由于定向突变压力降低而次生下降。
