Chédin F, Noirot P, Biaudet V, Ehrlich S D
Laboratoire de Génétique Microbienne, Institut National de Recherche Agronomique, Domaine de Vilvert, Jouy en Josas, France.
Mol Microbiol. 1998 Sep;29(6):1369-77. doi: 10.1046/j.1365-2958.1998.01018.x.
Homologous recombination in Bacillus subtilis requires the product of the addA and addB genes, the AddAB enzyme. This enzyme, which is both a helicase and a powerful nuclease, is thought to be the counterpart of the Escherichia coli RecBCD enzyme. From this analogy, it is expected that the nuclease activity of AddAB can be downregulated by a specific DNA sequence, which would correspond to the chi site in E. coli. Using protection of linear double-stranded DNA as a criterion, we identified the five-nucleotide sequence 5'-AGCGG-3', or its complement 5'-CCGCT-3', as being sufficient for AddAB nuclease attenuation. We have shown further that this attenuation occurs only if the sequence is properly oriented with respect to the translocating AddAB enzyme. Finally, inspection of the complete B. subtilis genome revealed that this five-nucleotide sequence is over-represented and is, in a majority of cases, co-oriented with DNA replication. Based on these observations, we propose that 5'-AGCGG-3', or its complement, is the B. subtilis analogue of the E. coli chi sequence.
枯草芽孢杆菌中的同源重组需要addA和addB基因的产物，即AddAB酶。这种酶既是解旋酶又是一种强大的核酸酶，被认为是大肠杆菌RecBCD酶的对应物。基于这种类比，预计AddAB的核酸酶活性可以被特定的DNA序列下调，这将对应于大肠杆菌中的chi位点。以线性双链DNA的保护作为标准，我们确定了五核苷酸序列5'-AGCGG-3'或其互补序列5'-CCGCT-3'足以使AddAB核酸酶衰减。我们进一步表明，只有当该序列相对于移位的AddAB酶正确定向时，才会发生这种衰减。最后，对完整的枯草芽孢杆菌基因组进行检查发现，这个五核苷酸序列出现的频率过高，并且在大多数情况下与DNA复制同向排列。基于这些观察结果，我们提出5'-AGCGG-3'或其互补序列是大肠杆菌chi序列在枯草芽孢杆菌中的类似物。
