Schünemann S, Schulte-Frohlinde D
Max-Planck-Institut für Strahlenchemie, Mülheim a.d. Ruhr, FRG.
Mol Gen Genet. 1992 Jun;233(3):348-54. doi: 10.1007/BF00265430.
The survival of M13 DNA was studied after partial replacement of thymine by uracil in the bacteriophage. Uracils carry the same genetic information as the thymines. Nevertheless in Escherichia coli wild-type cells, uracils in DNA are replaced by thymines by excision repair initiated by uracil-DNA glycosylase (UDG). Thus inactivation of uracil-containing phage DNA is solely due to repair initiated by UDG. Incorporation of uracils was achieved in one or in both strands, either randomly or site-specifically using differently uracylated oligonucleotides. The results show that up to 580 uracils can be repaired without a significant decrease in survival if the uracils are localized in the (-) strand only. Incorporation of 246 uracils into the (+) strand leads to approximately 30% or approximately 10% survival when expressed in Escherichia coli strains CMK and JM103, respectively. However, when uracils are distributed over both strands a sharp decrease in survival occurs. This shows that the repair of two uracils localized in close proximity on opposite strands of the DNA by the excision repair mechanism is difficult, whereas uracils occurring in one strand are repaired more efficiently, irrespective of their number.
在噬菌体中用尿嘧啶部分替代胸腺嘧啶后，对M13 DNA的存活情况进行了研究。尿嘧啶携带的遗传信息与胸腺嘧啶相同。然而，在大肠杆菌野生型细胞中，DNA中的尿嘧啶会被尿嘧啶-DNA糖基化酶（UDG）启动的切除修复替换为胸腺嘧啶。因此，含尿嘧啶的噬菌体DNA的失活完全是由于UDG启动的修复。使用不同的尿嘧啶化寡核苷酸，可随机或位点特异性地在一条链或两条链中掺入尿嘧啶。结果表明，如果尿嘧啶仅位于（-）链中，多达580个尿嘧啶可以被修复而存活率没有显著下降。当在大肠杆菌菌株CMK和JM103中表达时，在（+）链中掺入246个尿嘧啶分别导致约30%或约10%的存活率。然而，当尿嘧啶分布在两条链上时，存活率会急剧下降。这表明，通过切除修复机制修复位于DNA相反链上紧邻位置的两个尿嘧啶是困难的，而一条链中出现的尿嘧啶无论数量多少都能更有效地被修复。
