Asai T, Sommer S, Bailone A, Kogoma T
Department of Cell Biology, University of New Mexico School of Medicine, Albuquerque 87131.
EMBO J. 1993 Aug;12(8):3287-95. doi: 10.1002/j.1460-2075.1993.tb05998.x.
Escherichia coli cells induced for the SOS response express inducible stable DNA replication (iSDR) as an SOS function. Initiation of iSDR is independent of transcription, translation and DnaA protein, which are essential for initiation of DNA replication from oriC. We found that a recA mutant that is defective in recombination but proficient in SOS induction could not elicit iSDR. In contrast, iSDR was enhanced by recD and recJ mutations that inactivate the exonuclease V activity of the RecBCD enzyme and the RecJ exonuclease activity, respectively. A mutation in the ruvC gene that blocks the resolution of recombination intermediates (i.e. Holliday structures) also enhanced iSDR. Furthermore, inhibition of branch migration by recG or ruvAB mutations dramatically increased the iSDR activity. recBC mutants are defective in iSDR induction but the defect was suppressed by a mutation in the sbcA gene. The major product of minichromosomes replicated by iSDR was covalently closed circular monomers. We propose that recombination intermediates (i.e. D-loop structures) created by the action of RecA recombinase and RecBC(D) helicase play a central role in initiation of iSDR.
被诱导产生SOS应答的大肠杆菌细胞会表达可诱导的稳定DNA复制（iSDR）作为一种SOS功能。iSDR的起始独立于转录、翻译和DnaA蛋白，而这些对于从oriC起始DNA复制是必不可少的。我们发现，一个在重组方面有缺陷但在SOS诱导方面 proficient的recA突变体无法引发iSDR。相反，recD和recJ突变分别使RecBCD酶的核酸外切酶V活性和RecJ核酸外切酶活性失活，从而增强了iSDR。ruvC基因中的一个突变阻止了重组中间体（即霍利迪结构）的拆分，也增强了iSDR。此外，recG或ruvAB突变对分支迁移的抑制显著增加了iSDR活性。recBC突变体在iSDR诱导方面有缺陷，但该缺陷被sbcA基因中的一个突变所抑制。通过iSDR复制的微型染色体的主要产物是共价闭合环状单体。我们提出，由RecA重组酶和RecBC(D)解旋酶的作用产生的重组中间体（即D环结构）在iSDR的起始中起核心作用。
