C1 repressor-mediated DNA looping is involved in C1 autoregulation of bacteriophage P1

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Item Type:	Article
Title:	C1 repressor-mediated DNA looping is involved in C1 autoregulation of bacteriophage P1
Creators Name:	Heinzel, T., Lurz, R., Dobrinski, B., Velleman, M. and Schuster, H.
Abstract:	C1 repressor is required to repress the lytic functions of a P1 prophage in vivo. Transcription of the c1 gene is autoregulated via the C1-controlled operator Op99a,b which overlaps the promoter of the c1 gene. It is negatively affected by Lxc corepressor and the DNA region upstream of c1, which contains the additional operators Op99c, d, and e. We have explored these effects by constructing a set of lacZ reporter plasmids with Op99a,b and varying parts of the upstream DNA region. Transcription levels were measured in vivo with a two-plasmid system containing the lacZ reporter and a c1+ lxc+ or c1+ lxc- plasmid. Compared to the C1+Lxc-repressed lacZ reporter with all operators present, the basal level of beta-galactosidase activity increases successively when (i) upstream operators were deleted or inactivated, (ii) Lxc corepressor was removed, and (iii) C1 and Lxc were absent. By that means a 2 x 2 x 15-fold stepwise increase in enzyme activity was found. Using electron microscopy to visualize the interaction of C1 repressor with the operators in vitro, looped DNA molecules were observed. Although all operators can participate in C1-mediated DNA looping, loops between Op99a,b and Op99d occurred predominantly. Lxc is not required but increases drastically the frequency of loop formation. The results indicate that C1-mediated DNA looping may be a second element besides Lxc for fine-tuning the autoregulation of c1 transcription.
Keywords:	Bacteriophage P1, Base Sequence, DNA Primers, DNA-Binding Proteins, Electron Microscopy, Genetic Operator Regions, Genetic Transcription, Molecular Sequence Data, Site-Directed Mutagenesis, Messenger RNA, Repressor Proteins, Structure-Activity Relationship, Viral DNA, Viral Gene Expression Regulation, Viral Proteins
Source:	Journal of Biological Chemistry
ISSN:	0021-9258
Publisher:	American Society for Biochemistry and Molecular Biology
Volume:	269
Number:	50
Page Range:	31885-31890
Date:	16 December 1994
Official Publication:	http://www.jbc.org/content/269/50/31885.abstract
PubMed:	View item in PubMed

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