期刊
JOURNAL OF MOLECULAR BIOLOGY
卷 384, 期 3, 页码 577-589出版社
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2008.09.071
关键词
bistable genetic switch; CI repressor; cooperativity; transcriptional regulation; distant operator site O-D
资金
- Danish Council for Technology and Innovation
- Danish National Research Foundation
A genetic switch controls whether the temperate bacteriophage TP901-1 will enter a lytic or a lysogenic life cycle after infection of its host, Lactococcus lactis. We studied this bistable switch encoded in a small DNA fragment of 979 bp by fusing it to a reporter gene on a low-copy-number plasmid. The cloned DNA fragment contained the two divergently oriented promoters, P-R and P-L, transcribing the lysogenic and lytic gene clusters; the two promoter-. proximal genes, cl and mor; and the three CI operator sites, O-R, O-L and O-D. We show that mor encodes a protein and that this protein in concert with CI is required for the bistability. Furthermore, interaction of CI at O-R represses transcription from the lysogenic promoter, P-R. Thus, CI regulates its own transcription. Interaction of CI at O-L represses transcription from the lytic promoter, P-L. The presence of only O-L (absence of O-R and O-D) is enough to maintain a bistable system. The distantly located operator site, 01:), functions as a helper site by increasing binding of CI at O-R and O-L. In the immune state, O-D increases repression of the lytic promoter, P-L. Our results strongly support the model that a hexameric form of Cl binds cooperatively to the three operator sites in the immune state forming a CI-DNA loop structure. Finally, we show that in the anti-immune state, repression of the lysogenic promoter is independent of the known CI operator sites but requires the presence of both CI and MOR. (C) 2008 Elsevier Ltd. All rights reserved.
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