Edlund T, Normark S
Nature. 1981 Jul 16;292(5820):269-71. doi: 10.1038/292269a0.
The ampC gene of Escherichia coli K-12 codes for a beta-lactamase which can hydrolyse the beta-lactam ring of ampicillin. Ampicillin resistance is strictly related to ampC gene copy number thus we have been able to isolate ampicillin-resistant mutants carrying multiple ampC repeats. We have isolated on a plasmid a segment of chromosomal DNA carrying multiple ampC repeats, and compared the nucleotide sequence of the region joining repeat units to the sequence of the DNA segments that fused to create the joint. The fusion had occurred within a 12-base pair (bp) sequence of perfect homology. We suggest that recombination between randomly occurring short homologies (12-13-bp long), could be a general mechanism to generate tandem duplications in the size range of 10 kilobases (kb).
大肠杆菌K-12的ampC基因编码一种β-内酰胺酶，该酶可水解氨苄青霉素的β-内酰胺环。氨苄青霉素抗性与ampC基因拷贝数密切相关，因此我们能够分离出携带多个ampC重复序列的氨苄青霉素抗性突变体。我们在质粒上分离出一段携带多个ampC重复序列的染色体DNA片段，并将连接重复单元的区域的核苷酸序列与融合形成接头的DNA片段的序列进行了比较。融合发生在一个12个碱基对（bp）的完全同源序列内。我们认为，随机出现的短同源序列（12 - 13bp长）之间的重组可能是产生10千碱基（kb）大小范围内串联重复的一般机制。
