Barkovskiĭ E V, Khrustalev V V
Mol Gen Mikrobiol Virusol. 2009(1):16-21.
The purpose of this work was to find the character of the dependence between the GC-content of the gene and the level of preterminal codons usage inside it. 84 codon usage tables were used as the material (each of them contains average frequencies of codon usage for all encoding districts belonging to one bacterial specie). We also used nucleotide sequences encoding for active centers of bacterial adenylate cyclases. Inverse correlation between the GC-content (G+C) and the total level of preterminal codons usage (PCU) was observed (R = - 0.97). For nucleotide sequences encoding for active centers from adenylate cyclases class I the coefficient of correlation between G+C and PCU is -0.75. For sequences encoding for active centers from adenylate cyclases class III the coefficient of correlation between G+C and PCU is -0.91. Preterminal codons are mostly GC-deficient relative to their synonymous nonpreterminal codons and in absolute terms. The cause of the inverse correlation between G+C and the level of preterminal codons usage is an increase in their frequencies of usage due to mutational AT-pressure and the decrease of their frequencies of usage due to mutational GC-pressure. The evidence of the frequent fixation of nonsense mutations in GC-deficient bacteria was found. The practical conclusion is the following: the higher is the GC-content of gene or genome, the lower is the probability of nonsense mutation inside it.
这项工作的目的是找出基因的GC含量与其内部前末端密码子使用水平之间的依赖关系特征。84个密码子使用表被用作材料（每个表包含属于一种细菌物种的所有编码区的密码子使用平均频率）。我们还使用了编码细菌腺苷酸环化酶活性中心的核苷酸序列。观察到GC含量（G+C）与前末端密码子使用的总水平（PCU）之间呈负相关（R = - 0.97）。对于编码I类腺苷酸环化酶活性中心的核苷酸序列，G+C与PCU之间的相关系数为-0.75。对于编码III类腺苷酸环化酶活性中心的序列，G+C与PCU之间的相关系数为-0.91。相对于它们的同义非前末端密码子，前末端密码子在GC含量方面大多是不足的，并且从绝对值来看也是如此。G+C与前末端密码子使用水平之间负相关的原因是由于突变的AT压力导致其使用频率增加，以及由于突变的GC压力导致其使用频率降低。发现了GC含量不足的细菌中无义突变频繁固定的证据。实际结论如下：基因或基因组的GC含量越高，其中无义突变的概率就越低。
