The SOS response-associated peptidase (SRAP) is an ancient protein superfamily in all domains of life. The mammalian SRAP was recently reported to covalently bind to the abasic sites (AP) in single stranded (ss) DNA to shield the chromosome integrity. YedK, the Escherichia coli SRAP, is not functionally characterized. Here we report the fortuitous pull-down of YedK from bacterial cell lysates by short (<20 bp) double stranded (ds) DNAs, further enrichment of YedK was observed when single stranded (ss) DNA was added. YedK can bind multiple DNA substrates, particularly with a high affinity to DNA duplex with single strand segment. As a SRAP protein, the involvement of YedK in SOS response was extensively examined, however yedK mutant of Escherichia coli showed no difference from the wild type strain upon the treatments with UV and various DNA damaging reagents, indicating its non-essentiality or redundancy in E. coli. Surprisingly, yedK mutants derived from Escherichia coli and Samonella enterica both showed an increased plasmid DNA transformation efficiency compared to the wild types. In accordance with this, induction of YedK effectively decreased the copy number of plasmid DNA. Site-directed mutagenesis of YedK demonstrated that residues involved in single strand DNA binding and cysteine residue at position 2 from N-terminus can discharge the repression of the plasmid transformation efficiency.

SOS 反应相关肽酶 (SRAP) 是一个古老的蛋白质超家族，存在于生命的所有领域。最近有报道称哺乳动物 SRAP 与单链 (ss) DNA 中的脱碱基位点 (AP) 共价结合，以保护染色体的完整性。YedK，即大肠杆菌SRAP，没有功能特征。在这里，我们报告了通过短（<20 bp）双链（ds）DNA从细菌细胞裂解物中偶然下拉YedK，当添加单链（ss）DNA时观察到YedK的进一步富集。YedK 可以结合多种 DNA 底物，特别是对具有单链片段的 DNA 双链体具有高亲和力。作为一种 SRAP 蛋白，YedK 在 SOS 反应中的参与得到了广泛的研究，然而yedK大肠杆菌的突变体在用紫外线和各种 DNA 损伤试剂处理后，与野生型菌株没有区别，表明其在大肠杆菌中的非必需性或冗余性。令人惊讶的是，与野生型相比，源自大肠杆菌和肠沙门氏菌的yedK突变体均显示出更高的质粒 DNA 转化效率。据此，YedK的诱导有效地降低了质粒DNA的拷贝数。YedK的定点诱变表明，参与单链DNA结合的残基和N末端第2位的半胱氨酸残基可以解除对质粒转化效率的抑制。