Yang M K, Ser S C, Lee C H
Department of Biology, Fu-Jen University, Taipei, Taiwan, Republic of China.
Proc Natl Sci Counc Repub China B. 1989 Oct;13(4):276-83.
The effects of DNA methyltransferases on Tn3 transposition were investigated. The E. coli dam (deoxyadenosine methylase) gene was found to have no effect on Tn3 transposition. In contrast, Tn3 was found to transpose more frequently in dcm+ (deoxycytosine methylase) cells than in dcm- mutants. When the EcoRII methylase gene was introduced into dcm- cells (E. coli strain GM208), the frequency of Tn3 transposition in GM208 was dramatically increased. The EcoRII methylase recognizes and methylates the same sequence as does the dcm methylase. These results suggest that deoxycytosine methylase modified DNA may be a preferred target for Tn3 transposition. Experiments were also performed to determine whether the Tn3 transposase was involved in DNA modification. Plasmid DNA isolated from dcm- E. coli containing the Tn3 transposase gene was susceptible to ApyI digestion but resistant to EcoRI digestion, suggesting that Tn3 transposase modified the dcm recognition sequence. In addition, restriction enzymes TaqI, AvaII, BglI and HpaII did not digest this DNA completely, suggesting that the recognition sequences of TaqI, AvaII, BglI and HpaII were modified by Tn3 transposase to a certain degree. The type(s), the extent and mechanism(s) of this modification remain to be investigated.
研究了DNA甲基转移酶对Tn3转座的影响。发现大肠杆菌dam（脱氧腺苷甲基化酶）基因对Tn3转座没有影响。相反，发现Tn3在dcm +（脱氧胞嘧啶甲基化酶）细胞中比在dcm-突变体中转座更频繁。当将EcoRII甲基化酶基因导入dcm-细胞（大肠杆菌菌株GM208）时，GM208中Tn3转座的频率显著增加。EcoRII甲基化酶识别并甲基化与dcm甲基化酶相同的序列。这些结果表明，脱氧胞嘧啶甲基化酶修饰的DNA可能是Tn3转座的首选靶标。还进行了实验以确定Tn3转座酶是否参与DNA修饰。从含有Tn3转座酶基因的dcm-大肠杆菌中分离的质粒DNA对ApyI消化敏感，但对EcoRI消化有抗性，这表明Tn3转座酶修饰了dcm识别序列。此外，限制性内切酶TaqI、AvaII、BglI和HpaII不能完全消化这种DNA，这表明Tn3转座酶在一定程度上修饰了TaqI、AvaII、BglI和HpaII的识别序列。这种修饰的类型、程度和机制仍有待研究。
