期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1982
卷号：79
期号：16
页码：4907-4911
DOI：10.1073/pnas.79.16.4907
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：We have isolated lambda transducing phages carrying the Escherichia coli primase gene (dnaG) and mapped restriction sites in the cloned bacterial DNA segments. Several different DNA fragments containing the dnaG gene were inserted into multicopy plasmids. An analysis of the primase levels in cells harboring such plasmids indicates that sequences far upstream from the dnaG gene are required for optimal primase expression. Using this knowledge, we constructed a plasmid with a thermoinducible copy-number, pRLM61, which was employed to amplify intracellular primase levels approximately 100-fold. The dnaG gene is transcribed clockwise with respect to the E. coli genetic map, and a HindIII site located 180 base pairs upstream from the dnaG gene separates the gene from its primary promoter. An apparent transcription termination signal is positioned 30-70 base pairs in front of the primase gene. Transcription proceeds past this strong terminator only when RNA polymerase has first transcribed the bacterial DNA segment proximal to the HindIII site. We suggest that primase expression in E. coli is positively regulated by a mechanism of transcription antitermination mediated by a bacterial factor. We propose, furthermore, that the neighboring structural genes for primase and for the sigma subunit of RNA polymerase are coordinately regulated as part of an operon. This arrangement may enable the bacterial cell to readily control the level of initiation of DNA and RNA synthesis and thus to respond quickly and efficiently to changing conditions.
