Salles B, Paoletti C
Proc Natl Acad Sci U S A. 1983 Jan;80(1):65-9. doi: 10.1073/pnas.80.1.65.
The basal level of recA protein in Escherichia coli K-12 was estimated by an immunoradiometric assay; it is approximately equal to 1,200 molecules per wild-type bacteria in midexponential phase of growth, slightly more in an excision-deficient (uvrA) strain, and markedly more in recF mutants. Kinetics of induction after UV irradiation showed a rapid increase of recA protein content, which reached a peak level after 60-90 min (20- to 55-fold amplification) and then decreased by dilution of the protein in the growing population. In order to obtain an identical extent of induction of recA protein, a 10-fold higher UV dose was necessary in a wild-type strain compared to the uvrA mutant strain. In the uvrA strain, the presence of one or only very few pyrimidine dimers on DNA was accompanied by a measurable increase of the constitutive level of recA protein; however, the unexcised dimers were unable to permanently induce the formation of recA protein. The derepressed promoter of recA gene is one of the strongest in E. coli. Its sequence displays many similarities with that of the strongest early promoters of T5 phage. Mutants (umuC uvrB and recF uvrB) unable to carry out W-reactivation produced high levels of recA protein after UV irradiation. The data suggested that the recF and umuC genes negatively control the regulation of recA protein level.
通过免疫放射分析测定了大肠杆菌K-12中recA蛋白的基础水平；在生长对数中期，野生型细菌中约相当于每菌1200个分子，切除缺陷型（uvrA）菌株中的略多，recF突变体中的则明显更多。紫外线照射后的诱导动力学显示recA蛋白含量迅速增加，在60 - 90分钟后达到峰值水平（扩增20至55倍），然后在生长群体中因蛋白稀释而下降。为了获得相同程度的recA蛋白诱导，与uvrA突变株相比，野生型菌株所需的紫外线剂量要高10倍。在uvrA菌株中，DNA上存在一个或仅极少数嘧啶二聚体伴随着recA蛋白组成水平的可测量增加；然而，未切除的二聚体无法永久诱导recA蛋白的形成。recA基因的去阻遏启动子是大肠杆菌中最强的启动子之一。其序列与T5噬菌体最强的早期启动子序列有许多相似之处。无法进行W-复活的突变体（umuC uvrB和recF uvrB）在紫外线照射后产生高水平的recA蛋白。数据表明recF和umuC基因对recA蛋白水平的调节起负调控作用。
