Senear A W, Steitz J A
J Biol Chem. 1976 Apr 10;251(7):1902-12.
We have studied the interaction of the host factor (HF) required for bacteriophage Qbeta RNA replication and of ribosomal protein S1, a subunit of Qbeta replicase, with Qbeta and R17 RNA. Both proteins bind to both Qbeta and R17 RNA; HF has a higher affinity than S1 for these phages RNAs. HF binds to a single site in R17 RNA located in the replicase cistron, and to two sites of Qbeta RNA, one of which is located approximately 60 nucleotides from the 6' end of Qbeta RNA. The three HF binding sites all have portions rich in adenylate residues; all are bound by HF when contained in oligonucleotides which are predicted to exist only in single-stranded form. S1 selects a single site in Qbeta RNA, also near the 6' end, but binds to a large number of sites in R17 RNA. These results suggest that HF and possibly S1, through their interaction with the 3'-terminal region of Qbeta RNA, are directly involved in the recognition of the 6' end of Qbeta RNA by Qbeta replicase. Under conditions where specific protein-R1M RNA complexes are formed, we have also tested host factor and S1 for cistron-specific interference with ribosome binding to R17 RNA. Although S1 and HF lower the efficiency of initiation complex formation as described previously, we detect no discrimination against any particular cistron. We therefore conclude that translational interference exhibited by the two proteins probably reflects simply their high affinity for RNA and certain defined polynucleotides.
我们研究了噬菌体Qβ RNA复制所需的宿主因子（HF）以及Qβ复制酶的一个亚基核糖体蛋白S1与Qβ和R17 RNA的相互作用。这两种蛋白质都能与Qβ和R17 RNA结合；HF对这些噬菌体RNA的亲和力比S1更高。HF与位于复制酶顺反子中的R17 RNA的一个位点结合，与Qβ RNA的两个位点结合，其中一个位点距离Qβ RNA的6'端约60个核苷酸。这三个HF结合位点都有富含腺苷酸残基的部分；当包含在预计仅以单链形式存在的寡核苷酸中时，它们都能被HF结合。S1在Qβ RNA中选择一个也靠近6'端的位点，但与R17 RNA中的大量位点结合。这些结果表明，HF以及可能的S1通过与Qβ RNA的3'末端区域相互作用，直接参与了Qβ复制酶对Qβ RNA 6'端的识别。在形成特定蛋白质-R1M RNA复合物的条件下，我们还测试了宿主因子和S1对核糖体与R17 RNA结合的顺反子特异性干扰。尽管如前所述，S1和HF降低了起始复合物形成的效率，但我们没有检测到对任何特定顺反子的歧视。因此，我们得出结论，这两种蛋白质表现出的翻译干扰可能仅仅反映了它们对RNA和某些特定多核苷酸的高亲和力。
