Atkinson B L, Gottesman M E
Institute of Cancer Research, Columbia University, College of Physicians and Surgeons, New York, NY 10032.
J Mol Biol. 1992 Sep 5;227(1):29-37. doi: 10.1016/0022-2836(92)90679-e.
The lambdoid bacteriophage regulate gene expression by suppressing transcription terminators. Although similar in sequence to lambda, HK022 lacks an analogue to the lambda N antitermination gene and a distinct nutR sequence. To define the HK022 antitermination system, we plated the phage on Escherichia coli nus mutants that inhibit lambda N function. Only rpoB60 (also called nusC60) blocked HK022 lytic growth. Analyses of HK022-lambda hybrid phage suggested that a HK022 function analogous to lambda Q was inhibited by rpoB60. This result was confirmed with pR'-tR'-galK fusions. HK022 Q-protein suppressed tR' in wild-type but not in rpoB60 mutants. The lambda Q-protein, although inhibited by rpoB60, was more active than the HK022 analogue. A single amino acid difference between the two Q-proteins accounts for the phenotype. Changing the penultimate residue of HK022 Q from alanine to the lambda threonine generated a phage that could propagate on rpoB60 hosts. Host and phage mutations that permitted HK022 growth in rpoB60 strains were characterized. The bacterial suppressors were located in the Escherichia coli nusB gene. The phage suppressors represented recessive mutations in a HK022 b-region sequence encoding an open reading frame of 73 codons.
λ样噬菌体通过抑制转录终止子来调控基因表达。尽管HK022在序列上与λ相似，但它缺乏λ N抗终止基因的类似物和独特的nutR序列。为了确定HK022抗终止系统，我们将该噬菌体接种在抑制λ N功能的大肠杆菌nus突变体上。只有rpoB60（也称为nusC60）阻断了HK022的裂解生长。对HK022-λ杂交噬菌体的分析表明，rpoB60抑制了HK022中一个与λ Q功能类似的功能。这一结果通过pR'-tR'-galK融合得到了证实。HK022 Q蛋白在野生型中抑制tR'，但在rpoB60突变体中则不然。λ Q蛋白虽然受到rpoB60的抑制，但比HK022的类似物更具活性。两种Q蛋白之间的一个氨基酸差异解释了这种表型。将HK022 Q的倒数第二个残基从丙氨酸改变为λ的苏氨酸，产生了一种能够在rpoB60宿主上繁殖的噬菌体。对允许HK022在rpoB60菌株中生长的宿主和噬菌体突变进行了表征。细菌抑制因子位于大肠杆菌nusB基因中。噬菌体抑制因子代表了HK022 b区域序列中的隐性突变，该序列编码一个73个密码子的开放阅读框。
