Department of Biochemistry, Tel Aviv University, Tel Aviv 69978, Israel.
Virology. 2011 May 25;414(1):97-101. doi: 10.1016/j.virol.2011.03.022. Epub 2011 Apr 9.
The anticodon nuclease (ACNase) PrrC is silenced in Escherichia coli by an associated DNA restriction-modification protein, activated by the phage T4-encoded anti-DNA restriction factor Stp and counteracted by T4's tRNA repair enzymes polynucleotide kinase and RNA ligase 1. Hence, only tRNA repair-deficient phages succumb to PrrC's restriction. PrrC's ABC-ATPase motor domains are implicated in driving its activation by hydrolyzing GTP and in stabilizing the activated ACNase by avidly binding dTTP. The latter effect has been associated with dTTP's accumulation early in T4 infection when PrrC is activated. In agreement, delayed dTTP accumulation caused by dCMP deaminase deficiency coincided with impaired manifestation of PrrC's ACNase activity. This impairment did not suffice to suppress the PrrC-mediated restriction of tRNA repair deficient phage but was synthetically suppressive with a leaky stp mutation that only partly impairs PrrC's activation. Presumably, ability to gauge dTTP's changing level helps confine PrrC's toxicity to its viral target.
反密码子核酸内切酶（ACNase）PrrC 由与之相关联的 DNA 限制修饰蛋白所沉默，被噬菌体 T4 编码的抗 DNA 限制因子 Stp 激活，并被 T4 的 tRNA 修复酶多核苷酸激酶和 RNA 连接酶 1 拮抗。因此，只有 tRNA 修复缺陷的噬菌体才会屈服于 PrrC 的限制。PrrC 的 ABC-ATPase 马达结构域被认为通过水解 GTP 来驱动其激活，并通过强烈结合 dTTP 来稳定激活的 ACNase。当 PrrC 被激活时，这种效应与 T4 感染早期 dTTP 的积累有关。一致地，由于 dCMP 脱氨酶缺陷导致的 dTTP 积累延迟，与 PrrC 的 ACNase 活性的受损表现一致。这种损伤不足以抑制 PrrC 介导的对 tRNA 修复缺陷噬菌体的限制，但与漏失的 stp 突变具有合成抑制作用，该突变仅部分损害 PrrC 的激活。推测，衡量 dTTP 变化水平的能力有助于将 PrrC 的毒性限制在其病毒靶标上。
