Birkeland N K, Lindqvist B H, Christie G E
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond 23298-0698.
J Bacteriol. 1991 Nov;173(21):6927-34. doi: 10.1128/jb.173.21.6927-6934.1991.
The bacteriophage P2 ogr gene encodes an 8.3-kDa protein that is a positive effector of P2 late gene transcription. The ogr gene is preceded by a promoter sequence (Pogr) resembling a normal Escherichia coli promoter and is located just downstream of a late transcription unit. We analyzed the kinetics and regulation of ogr gene transcription by using an ogr-specific antisense RNA probe in an S1 mapping assay. During a normal P2 infection, ogr gene transcription starts from Pogr at an intermediate time between the onset of early and late transcription. At late times after infection the ogr gene is cotranscribed with the late FETUD operon; the ogr gene product thus positively regulates its own synthesis from the P2 late promoter PF. Expression of the P2 late genes also requires P2 DNA replication. Complementation experiments and transcriptional analysis show that a nonreplicating P2 phage expresses the ogr gene from Pogr but is unable to transcribe the late genes. A P2 ogr-defective phage makes an increased level of ogr mRNA, consistent with autogenous control from Pogr. Transcription of the ogr gene in the prophage of a P2 heteroimmune lysogen is stimulated after infection with P2, suggesting that Pogr is under indirect immunity control and is activated by a yet-unidentified P2 early gene product during infection.
噬菌体P2的ogr基因编码一种8.3千道尔顿的蛋白质，它是P2晚期基因转录的正效应物。ogr基因之前有一个类似于正常大肠杆菌启动子的启动子序列（Pogr），且位于一个晚期转录单元的下游。我们在S1作图分析中使用ogr特异性反义RNA探针分析了ogr基因转录的动力学和调控。在正常的P2感染过程中，ogr基因转录在早期和晚期转录开始之间的中间时间从Pogr起始。感染后期，ogr基因与晚期FETUD操纵子共转录；因此，ogr基因产物从P2晚期启动子PF正向调节其自身的合成。P2晚期基因的表达也需要P2 DNA复制。互补实验和转录分析表明，一个非复制性的P2噬菌体从Pogr表达ogr基因，但无法转录晚期基因。一个P2 ogr缺陷型噬菌体产生的ogr mRNA水平增加，这与来自Pogr的自身调节一致。用P2感染后，P2异源免疫溶原菌原噬菌体中ogr基因的转录受到刺激，这表明Pogr处于间接免疫控制之下，并在感染期间被一个尚未鉴定的P2早期基因产物激活。
