Synergism of mutations in bacteriophage Qbeta RNA affecting host factor dependence of Qbeta replicase.
Synergism of mutations in bacteriophage Qbeta RNA affecting host factor dependence of Qbeta replicase.
复制标题
噬菌体 Qbeta RNA 突变的协同作用影响 Qbeta 复制酶的宿主因子依赖性。
DOI：
10.1006/jmbi.1999.3373
复制
发表时间：
2000
影响因子：
5.6
通讯作者：
H. Weber
中科院分区：
文献类型：
--
作者：
D. Schuppli;J. Georgijevic;H. Weber
我们最近的研究表明，缺乏Hfq蛋白（即Qbeta“宿主因子”）的大肠杆菌细胞支持噬菌体Qbeta复制的效率低下，但噬菌体在突变宿主中迅速进化，基本上不依赖于宿主因子。在三个独立的适应实验中，一组相同的四个点突变被确定为适应表型的原因。在这里，我们报道了单个突变和它们的一些组合对噬菌体在体内增殖的宿主因子依赖性和qβ复制酶在体外复制噬菌体RNA的影响。我们发现每一个单一的替换只产生很小的影响，但这四个突变的组合协同解释了大多数观察到的进化噬菌体的适应性。令人惊讶的是，对适应噬菌体的3'端序列的重新分析导致在所有三个独立进化的噬菌体群体中发现了第五个突变，即核苷酸4214的C到U残基转变。这种突变以前被忽略了，因为它的位置离3'端只有三个核苷酸。它似乎对Hfq的独立性贡献不大，但可能通过重新建立涉及直接3'端序列的长距离碱基配对相互作用的可能性来增强RNA的稳定性。
We have recently shown that Escherichia coli cells deficient in Hfq protein (i.e. the Qbeta "host factor") support bacteriophage Qbeta replication inefficiently, but that the phage evolves rapidly in the mutant host to become essentially host factor independent. An identical set of four point mutations was identified as being responsible for the adapted phenotype in each of three independent adaptation experiments. Here we report the effects of the single mutations and of some of their combinations on host factor dependence of phage multiplication in vivo and of phage RNA replication by Qbeta replicase in vitro. We find that each single substitution produces only small effects, but that in combination the four mutations synergistically account for most of the observed adaptation of the evolved phages. Surprisingly, a reanalysis of the 3'-terminal sequence of the adapted phages resulted in the discovery of a fifth mutation in all three independently evolved phage populations, namely, a C to U residue transition at nucleotide 4214. This mutation had been missed previously because of its location only three nucleotides from the 3'-end. It appears to contribute little to the Hfq independence but may enhance RNA stability by re-establishing the possibility of forming a long-range base-pairing interaction involving the immediate 3'-terminal sequence.