Abraham J, Mascarenhas D, Fischer R, Benedik M, Campbell A, Echols H
Proc Natl Acad Sci U S A. 1980 May;77(5):2477-81. doi: 10.1073/pnas.77.5.2477.
The cII and cIII proteins specified by bacteriophage lambda direct the lysogenic response to infection through the coordinate establishment of repression and integration of the viral DNA. The regulatory activity of cII/cIII involves positive regulation of two promoter sites: the p(E) promoter, turning on expression of the cI protein that maintains lysogeny, and the p(I) promoter, activating synthesis of the Int protein for integrative recombination. Regulation of the p(I) promoter provides for differential expression of the Int protein with respect to the excision-specific Xis protein from the closely linked int and xis genes. We have determined the DNA sequence of the p(I) promoter region for wild-type lambda DNA and for two classes of mutations: intc mutations, which result in a high rate of Int synthesis in the absence of cII, and deletion mutations, some of which eliminate cII-activated expression of the int gene. We find a sequence with considerable homology (11 of 15 bases) to a "typical" (computer-generated) promoter sequence, adjacent to a region with striking homology (11 of 14 bases) to part of the p(E) promoter region. This presumed p(I) sequence overlaps the start of the xis gene and includes the site of two intc point mutations. A cII-insensitive xis(+) deletion partially removes the proposed p(I) sequence; a deletion that leaves the p(I) sequence intact but terminates 21 bases upstream does not interfere with cII activation of the int gene. From our results and the analysis of the p(E) region, we suggest that cII acts in the promoter -35 recognition region to facilitate binding by RNA polymerase at the -10 interaction region. Differential expression of the int and xis genes results because the p(I) transcript lacks the initiation codon for Xis protein synthesis.
噬菌体λ指定的cII和cIII蛋白通过病毒DNA阻遏和整合的协同建立，指导对感染的溶原反应。cII/cIII的调节活性涉及对两个启动子位点的正向调节：p(E)启动子，开启维持溶原性的cI蛋白的表达；p(I)启动子，激活用于整合重组的Int蛋白的合成。p(I)启动子的调节使得Int蛋白相对于来自紧密连锁的int和xis基因的切除特异性Xis蛋白有差异表达。我们已经确定了野生型λDNA以及两类突变的p(I)启动子区域的DNA序列：intc突变，其在没有cII的情况下导致Int的高合成率；缺失突变，其中一些消除了cII激活的int基因表达。我们发现一个与“典型”（计算机生成）启动子序列有相当同源性（15个碱基中有11个）的序列，与一个与p(E)启动子区域的一部分有显著同源性（14个碱基中有11个）的区域相邻。这个假定的p(I)序列与xis基因的起始重叠，并包括两个intc点突变的位点。一个对cII不敏感的xis(+)缺失部分去除了提议的p(I)序列；一个使p(I)序列完整但在其上游21个碱基处终止的缺失并不干扰cII对int基因的激活。根据我们的结果以及对p(E)区域的分析，我们认为cII在启动子的-35识别区域起作用，以促进RNA聚合酶在-10相互作用区域的结合。int和xis基因的差异表达是因为p(I)转录本缺乏Xis蛋白合成的起始密码子。
