Lida S, Marcoli R, Bickle T A
EMBO J. 1982;1(6):755-9. doi: 10.1002/j.1460-2075.1982.tb01242.x.
We have physically characterised a deletion mutant of the R plasmid R100 which has lost all of the antibiotic resistances, including chloramphenicol resistance (Cmr), coded by its IS1-flanked r-determinant. The deletion was mediated by one of the flanking IS1 elements and terminates within the carboxyl terminus of the Cmr gene. DNA sequence analysis showed that the mutated gene would produce a protein 20 amino acids longer than the wild-type due to fusion with an open reading frame in the IS element. Surprisingly for a deletion mutation, rare, spontaneous Cmr revertants could be recovered. Two of the four revertants studied had frame shifts due to the insertion of a single AT base pair at the same position; the revertants would code for a protein five amino acids shorter than the wild-type. The other two revertants had acquired duplications of the 34-bp inverted terminal repeat sequences of the IS1 element and would direct the synthesis of a protein six amino acids longer than the wild-type. The reverted Cmr markers were still capable of transposition. These observations suggest a role for point mutations and small DNA rearrangements in the formation of new gene organisations produced by mobile genetic elements.
我们对R质粒R100的一个缺失突变体进行了物理特性分析，该突变体已丧失了所有抗生素抗性，包括由其IS1侧翼的r决定簇编码的氯霉素抗性（Cmr）。缺失是由侧翼的IS1元件之一介导的，并在Cmr基因的羧基末端内终止。DNA序列分析表明，由于与IS元件中的一个开放阅读框融合，突变基因产生的蛋白质比野生型长20个氨基酸。令人惊讶的是，对于一个缺失突变，能够获得罕见的自发Cmr回复突变体。所研究的四个回复突变体中有两个由于在同一位置插入了单个AT碱基对而发生了移码；这些回复突变体编码的蛋白质比野生型短五个氨基酸。另外两个回复突变体获得了IS1元件34 bp反向末端重复序列的重复，并将指导合成比野生型长六个氨基酸的蛋白质。回复的Cmr标记仍然能够转座。这些观察结果表明点突变和小DNA重排在由移动遗传元件产生的新基因组织形成中起作用。
