Horizontal gene transfer contributes to the wide distribution and evolution of type II restriction-modification systems
Horizontal gene transfer contributes to the wide distribution and evolution of type II restriction-modification systems
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DOI：
10.1007/bf02198833
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发表时间：
1996-02-01
影响因子：
3.9
通讯作者：
Pingoud, A
中科院分区：
文献类型：
--
作者：
Jeltsch, A;Pingoud, A
限制性内切修饰（RM）系统可以保护细菌免受噬菌体的侵害。它们包括特异性切割DNA的限制性内切酶活性和特异性甲基化DNA的相应甲基转移酶活性，从而保护DNA免受切割。这种系统在细菌中很常见。为了找出RM系统的广泛分布是否由于水平基因转移，我们将29种II型RM系统的密码子使用情况与其各自细菌宿主的平均密码子使用情况进行了比较。在EcoRI、EcoRV、KpnI、SinI、smi和thhb81 6例中发现密码子使用明显偏差。在这些病例中，它们被解释为水平基因转移的证据。由于该方法预计只能检测到所有水平基因转移事件的四分之一到三分之一，这一结果意味着水平基因转移对RM系统的分布和进化有相当大的影响。在所有这六种情况下，限制性内切酶基因的密码子使用偏差比甲基转移酶基因的密码子使用偏差要明显得多。这一结果表明，在这些情况下，水平基因转移是依次发生的，甲基转移酶基因首先被细胞获得。这可以解释为，活性限制性内切酶对DNA不受相应甲基转移酶切割保护的细胞具有高毒性。
Restriction modification (RM) systems serve to protect bacteria against bacteriophages. They comprise a restriction endonuclease activity that specifically cleaves DNA and a corresponding methyltransferase activity that specifically methylates the DNA, thereby protecting it from cleavage. Such systems are very common in bacteria. To fmd out whether the widespread distribution of RM systems is due to horizontal gene transfer, we have compared the codon usages of 29 type II RM systems with the average codon usage of their respective bacterial hosts. Pronounced deviations in codon usage were found in six cases: EcoRI, EcoRV, KpnI, SinI, SmaI, and TthHB81. They are interpreted as evidence for horizontal gene transfer in these cases. As the methodology is expected to detect only one-fourth to one-third of all horizontal gene transfer events, this result implies that horizontal gene transfer had a considerable influence on the distribution and evolution of RM systems. In all of these six cases the codon usage deviations of the restriction enzyme genes are much more pronounced than those of the methyltransferase genes. This result suggests that in these cases horizontal gene transfer had occurred sequentially with the gene for the methyltransferase being first acquired by the cell. This can be explained by the fact that an active restriction endonuclease is highly toxic in cells whose DNA is not protected from cleavage by a corresponding methyltransferase.