Bissler J J, Meng Q S, Emery T
The Children's Hospital Research Foundation, Cincinnati, Ohio, USA.
Mol Med. 1998 Dec;4(12):795-806.
Mutations disrupting the function or production of C1 inhibitor cause the disease hereditary angioneurotic edema. Patient mutations identified an imperfect inverted repeat sequence that was postulated to play a mechanistic role in the mutations. To test this hypothesis, the inverted repeat was cloned into the chloramphenicol acetyltransferase gene in pBR325 and its mutation rate was studied in four bacterial strains. These strains were selected to assay the effects of recombination and superhelical tension on mutation frequency. Mutations that revert bacteria to chloramphenicol resistance (Cmr) were scored. Both pairs of isogenic strains had reversion frequencies of approximately 10(-8). These rare reversion events in bacteria were most often a frameshift that involved the imperfect inverted repeat with a deletion or a tandem duplication, an event very similar to the human mutations. Increased DNA superhelical tension, which would be expected to enhance cruciform extrusion, did not accentuate mutagenesis. This finding suggests that the imperfect inverted repeat may form a stem-loop structure in the single-stranded DNA created by the duplex DNA melting prior to replication. Models explaining the slippage can be drawn using the lagging strand of the replication fork. In this model, the formation of a stem-loop structure is responsible for bringing the end of the deletion or duplication into close proximity.
破坏C1抑制剂功能或产生的突变会导致遗传性血管性水肿疾病。患者突变鉴定出一个不完美的反向重复序列，推测该序列在突变中起机制性作用。为了验证这一假设，将反向重复序列克隆到pBR325中的氯霉素乙酰转移酶基因中，并在四种细菌菌株中研究其突变率。选择这些菌株来测定重组和超螺旋张力对突变频率的影响。对使细菌恢复氯霉素抗性（Cmr）的突变进行评分。这两对同基因菌株的回复频率均约为10^(-8)。细菌中这些罕见的回复事件最常见的是移码突变，涉及不完美的反向重复序列，伴有缺失或串联重复，这一事件与人类突变非常相似。预期会增强十字形挤出的增加的DNA超螺旋张力并未加剧诱变作用。这一发现表明，不完美的反向重复序列可能在复制前双链DNA解链产生的单链DNA中形成茎环结构。可以使用复制叉的后随链绘制解释滑动的模型。在这个模型中，茎环结构的形成负责使缺失或重复的末端紧密靠近。
