Bacteriophage Mu late promoters: four late transcripts initiate near a conserved sequence.
Bacteriophage Mu late promoters: four late transcripts initiate near a conserved sequence.
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噬菌体 Mu 晚期启动子：四个晚期转录物在保守序列附近起始。
DOI：
10.1128/jb.171.4.2003-2018.1989
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发表时间：
1989
影响因子：
3.2
通讯作者：
Howe,MM
中科院分区：
文献类型：
--
作者：
Margolin,W;Rao,G;Howe,MM
噬菌体 Mu 的后期转录导致噬菌体形态发生功能的表达，依赖于 Mu C 蛋白。早期实验表明 Mu 晚期 RNA 起源于四个启动子，包括之前表征的 mom 启动子。 S1 核酸酶保护实验用于绘制三个新区域中 RNA 5' 末端的图谱。只有在 C 存在的情况下，转录本才会在这些点上启动，并在 Mu 基因组上以向右的方向合成。质粒克隆的 Amber 突变标记救援分析和有限的 DNA 测序表明，这些新启动子位于 N 基因内的 C 和 lys 之间、I 上游和 P 上游。比较四个 RNA 5' 端上游的启动子序列，得到两个保守序列：第一个序列（tA . . cT，其中大写字母和小写字母分别表示 100% 和 75% 碱基保守性），位于大约 -10 处，与共有的大肠杆菌 sigma 70 -10 区域具有一些相似性，而第二个序列（ccATAAc CcCPuG/Cac，其中 Pu 表示嘌呤）位于-35 区域，与大肠杆菌 -35 共识没有相似之处。我们认为这些保守的 Mu 晚期启动子共有序列对于 C 依赖性启动子活性很重要。含有这些晚期启动子与 lacZ 转录融合的质粒在体内表现出 C 依赖性 β-半乳糖苷酶合成，并且 C 是该反式激活所需的唯一 Mu 产物。正如预期的那样，晚期启动子-lacZ 融合体仅在 Mu 原噬菌体诱导后的晚期才被激活。仅含有 Mu 晚期 RNA 5' 端几个碱基的 lacZ 融合体的 C 依赖性激活和改变的启动子序列的存在意味着 C 在转录起始水平起作用。
Late transcription of bacteriophage Mu, which results in the expression of phage morphogenetic functions, is dependent on Mu C protein. Earlier experiments indicated that Mu late RNAs originate from four promoters, including the previously characterized mom promoter. S1 nuclease protection experiments were used to map RNA 5' ends in the three new regions. Transcripts were initiated at these points only in the presence of C and were synthesized in a rightward direction on the Mu genome. Amber mutant marker rescue analysis of plasmid clones and limited DNA sequencing demonstrated that these new promoters are located between C and lys, upstream of I, and upstream of P within the N gene. A comparison of the promoter sequences upstream from the four RNA 5' ends yielded two conserved sequences: the first (tA . . cT, where capital and lowercase letters indicate 100 and 75% base conservation, respectively), at approximately -10, shares some similarity with the consensus Escherichia coli sigma 70 -10 region, while the second (ccATAAc CcCPuG/Cac, where Pu indicates a purine), in the -35 region, bears no resemblance to the E. coli -35 consensus. We propose that these conserved Mu late promoter consensus sequences are important for C-dependent promoter activity. Plasmids containing transcription fusions of these late promoters to lacZ exhibited C-dependent beta-galactosidase synthesis in vivo, and C was the only Mu product needed for this transactivation. As expected, the late promoter-lacZ fusions were activated only at late times after induction of a Mu prophage. The C-dependent activation of lacZ fusions containing only a few bases of the 5' end of Mu late RNA and the presence of altered promoter sequences imply that C acts at the level of transcription initiation.