Kelly T J, Simancek P, Brush G S
Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21210, USA.
Proc Natl Acad Sci U S A. 1998 Dec 8;95(25):14634-9. doi: 10.1073/pnas.95.25.14634.
Single-stranded DNA-binding proteins (SSBs) play essential roles in DNA replication, recombination, and repair in bacteria and eukarya. We report here the identification and characterization of the SSB of an archaeon, Methanococcus jannaschii. The M. jannaschii SSB (mjaSSB) has significant amino acid sequence similarity to the eukaryotic SSB, replication protein A (RPA), and contains four tandem repeats of the core single-stranded DNA (ssDNA) binding domain originally defined by structural studies of RPA. Homologous SSBs are encoded by the genomes of other archaeal species, including Methanobacterium thermoautotrophicum and Archaeoglobus fulgidus. The purified mjaSSB binds to ssDNA with high affinity and selectivity. The apparent association constant for binding to ssDNA is similar to that of RPA under comparable experimental conditions, and the affinity for ssDNA exceeds that for double-stranded DNA by at least two orders of magnitude. The binding site size for mjaSSB is approximately 20 nucleotides. Given that RPA is related to mjaSSB at the sequence level and to Escherichia coli SSB at the structural level, we conclude that the SSBs of archaea, eukarya, and bacteria share a common core ssDNA-binding domain. This ssDNA-binding domain was presumably present in the common ancestor to all three major branches of life.
单链DNA结合蛋白（SSB）在细菌和真核生物的DNA复制、重组及修复过程中发挥着至关重要的作用。我们在此报告了嗜热栖热菌（Methanococcus jannaschii）单链DNA结合蛋白的鉴定与特性研究。嗜热栖热菌单链DNA结合蛋白（mjaSSB）与真核生物单链DNA结合蛋白复制蛋白A（RPA）具有显著的氨基酸序列相似性，并且包含四个串联重复的核心单链DNA（ssDNA）结合结构域，该结构域最初是通过对RPA的结构研究确定的。其他古菌物种的基因组也编码同源的单链DNA结合蛋白，包括嗜热自养甲烷杆菌（Methanobacterium thermoautotrophicum）和嗜热栖热菌（Archaeoglobus fulgidus）。纯化后的mjaSSB以高亲和力和选择性结合单链DNA。在可比的实验条件下，其与单链DNA结合的表观缔合常数与RPA相似，且对单链DNA的亲和力比对双链DNA的亲和力至少高出两个数量级。mjaSSB的结合位点大小约为20个核苷酸。鉴于RPA在序列水平上与mjaSSB相关，在结构水平上与大肠杆菌单链DNA结合蛋白（Escherichia coli SSB）相关，我们得出结论，古菌、真核生物和细菌的单链DNA结合蛋白共享一个共同的核心单链DNA结合结构域。这个单链DNA结合结构域可能存在于生命三大主要分支的共同祖先中。
