Robledo R, Atkinson B L, Gottesman M E
Institute of Cancer Research, Columbia University College of Physicians and Surgeons, New York, NY 10032.
J Mol Biol. 1991 Aug 5;220(3):613-9. doi: 10.1016/0022-2836(91)90104-e.
The nun gene product of the lambdoid coliphage HK022 provokes premature transcription termination at, or near, the phage lambda nut sites. Termination by Nun and antitermination by lambda N protein both require the nut sites and Escherichia coli NusA, NusB and NusE proteins. To characterize further the host requirements for Nun termination, we selected host mutations that blocked termination at lambda nutR. In addition to mutations in nusA, nusB and nusE, we obtained mutations in rpoC, encoding the RNA polymerase beta' subunit. The nusA and rpoC mutations suppressed Nun termination but not antitermination by lambda N function. The mutations antagonized Nun only at lambda nutR; termination at lambda nutL occurred in all the mutant strains. Thus, nutL is not functionally equivalent to nutR. We conclude that the host requirements for Nun termination overlap but are not identical with those for N antitermination, and, in particular, that the beta' subunit of RNP may be Nun-specific.
λ样大肠杆菌噬菌体HK022的Nun基因产物会在噬菌体λ nut位点处或其附近引发过早的转录终止。Nun介导的终止和λ N蛋白介导的抗终止都需要nut位点以及大肠杆菌的NusA、NusB和NusE蛋白。为了进一步表征Nun终止对宿主的需求，我们筛选了能阻止在λ nutR处终止的宿主突变体。除了nusA、nusB和nusE中的突变外，我们还获得了编码RNA聚合酶β'亚基的rpoC中的突变。nusA和rpoC突变抑制了Nun终止，但没有抑制λ N功能介导的抗终止。这些突变仅在λ nutR处拮抗Nun；在所有突变菌株中均发生了在λ nutL处的终止。因此，nutL在功能上不等同于nutR。我们得出结论，Nun终止对宿主的需求有重叠，但与N抗终止的需求并不相同，特别是，RNP的β'亚基可能是Nun特异性的。
