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

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 con...

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Bibliographic Details
Published in:The Journal of biological chemistry 1994-12, Vol.269 (50), p.31885-31890
Main Authors: Heinzel, T, Lurz, R, Dobrinski, B, Velleman, M, Schuster, H
Format: Article
Language:English
Subjects:
Bacteriophage P1 - genetics
Base Sequence
DNA Primers - chemistry
DNA, Viral - metabolism
DNA, Viral - ultrastructure
DNA-Binding Proteins - metabolism
Gene Expression Regulation, Viral
Microscopy, Electron
Molecular Sequence Data
Mutagenesis, Site-Directed
Operator Regions, Genetic
phage P1
Repressor Proteins - genetics
RNA, Messenger - genetics
Structure-Activity Relationship
Transcription, Genetic
Viral Proteins - genetics
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Summary: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.
ISSN:0021-9258
1083-351X
DOI:10.1016/S0021-9258(18)31778-2