Emilsson V, Kurland C G
Department of Molecular Biology, Uppsala University.
EMBO J. 1990 Dec;9(13):4359-66. doi: 10.1002/j.1460-2075.1990.tb07885.x.
We have tested the predictions of a model that accounts for the codon preferences of bacteria in terms of a growth maximization strategy. According to this model the tRNA species cognate to minor and major codons should be regulated differently under different growth conditions: the isoacceptors cognate to major codons should increase at fast growth rates while those cognate to minor codons should decrease at fast growth rates. We have used a quantitative Northern blotting technique to measure the abundance of the methionine and the leucine isoacceptor families over growth rates ranging from 0.5 to 2.1 doublings per hour. Five tRNA species that are cognate to major codons (tRNA(eMet), tRNA(1fMet), tRNA(2fMet), tRNA(1Leu) and tRNA(3Leu) increase both as a relative fraction of total tRNA and in absolute concentration with increasing growth rates. Three tRNA species that are cognate to minor codons (tRNA(2Leu), tRNA(4Leu) and tRNA(5Leu) decrease as a relative fraction of total RNA and in absolute concentration with increasing growth rates. These data suggest that the abundances of groups of tRNA species are regulated in different ways, and that they are not regulated simply according to isoacceptor specificity. In particular, the data support the growth optimization model for codon bias.
我们测试了一个模型的预测结果，该模型从生长最大化策略的角度解释了细菌的密码子偏好。根据这个模型，在不同生长条件下，与次要和主要密码子对应的tRNA种类应该受到不同的调节：与主要密码子对应的同功受体在快速生长速率下应该增加，而与次要密码子对应的同功受体在快速生长速率下应该减少。我们使用定量Northern印迹技术，测量了在每小时0.5至2.1次倍增的生长速率范围内，甲硫氨酸和亮氨酸同功受体家族的丰度。与主要密码子对应的5种tRNA种类（tRNA(eMet)、tRNA(1fMet)、tRNA(2fMet)、tRNA(1Leu)和tRNA(3Leu)）作为总tRNA的相对比例以及绝对浓度，都随着生长速率的增加而增加。与次要密码子对应的3种tRNA种类（tRNA(2Leu)、tRNA(4Leu)和tRNA(5Leu)）作为总RNA的相对比例以及绝对浓度，都随着生长速率的增加而减少。这些数据表明，tRNA种类组的丰度以不同方式受到调节，而且它们并非仅仅根据同功受体特异性进行调节。特别是，这些数据支持了密码子偏好的生长优化模型。
