Amitsur M, Morad I, Chapman-Shimshoni D, Kaufmann G
Department of Biochemistry, Tel Aviv University, Ramat Aviv, Israel.
EMBO J. 1992 Aug;11(8):3129-34. doi: 10.1002/j.1460-2075.1992.tb05385.x.
Phage T4-induced anticodon nuclease triggers cleavage-ligation of the host tRNA(Lys). The enzyme is encoded in latent form by the optional Escherichia coli locus prr and is activated by the product of the phage stp gene. Anticodon nuclease latency is attributed to the masking of the core function prrC by flanking elements homologous with type I restriction-modification genes (prrA-hsdM and prrD-hsdR). Activation of anticodon nuclease in extracts of uninfected prr+ cells required synthetic Stp, ATP and GTP and appeared to depend on endogenous DNA. Stp could be substituted by a small, heat-stable E. coli factor, hinting that anticodon nuclease may be mobilized in cellular situations other than T4 infection. Hsd antibodies recognized the anticodon nuclease holoenzyme but not the prrC-encoded core. Taken together, these data indicate that Hsd proteins partake in the latent ACNase complex where they mask the core factor PrrC. Presumably, this masking interaction is disrupted by Stp in conjunction with Hsd ligands. The Hsd-PrrC interaction may signify coupling and mutual enhancement of two prokaryotic restriction systems operating at the DNA and tRNA levels.
噬菌体T4诱导的反密码子核酸酶引发宿主tRNA（Lys）的切割-连接。该酶以潜伏形式由大肠杆菌可选基因座prr编码，并被噬菌体stp基因的产物激活。反密码子核酸酶的潜伏性归因于与I型限制修饰基因（prrA-hsdM和prrD-hsdR）同源的侧翼元件对核心功能prrC的掩盖。在未感染的prr+细胞提取物中激活反密码子核酸酶需要合成的Stp、ATP和GTP，并且似乎依赖于内源性DNA。Stp可以被一种小的、热稳定的大肠杆菌因子替代，这表明反密码子核酸酶可能在除T4感染之外的细胞情况下被激活。Hsd抗体识别反密码子核酸酶全酶，但不识别prrC编码的核心。综上所述，这些数据表明Hsd蛋白参与潜伏的ACNase复合物，在其中它们掩盖核心因子PrrC。据推测，这种掩盖相互作用被Stp与Hsd配体共同破坏。Hsd-PrrC相互作用可能意味着在DNA和tRNA水平上运行的两个原核限制系统的耦合和相互增强。
