Cooperativity in long-range gene regulation by the λ CI repressor (original) (raw)
- Ian B. Dodd1,3,
- Keith E. Shearwin1,
- Alison J. Perkins1,
- Tom Burr2,
- Ann Hochschild2, and
- J. Barry Egan1
- 1Discipline of Biochemistry, School of Molecular and Biomedical Science, University of Adelaide, South Australia 5005, Australia;2Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA
Abstract
Effective repression of cI transcription from _P_RM by the bacteriophage λ CI repressor requires binding sites (_O_L) located 2.4 kb from the promoter. A CI tetramer bound to O_L1.O_L2 interacts with a tetramer bound near _P_RM (O_R1.O_R2), looping the intervening DNA. We previously proposed that in this CI octamer:DNA complex, the distant _O_L3 operator and the weak _O_R3 operator overlapping _P_RM are juxtaposed so that a CI dimer at _O_L3 can cooperate with a CI dimer binding to _O_R3. Here we show that _O_L3 is necessary for effective repression of _P_RM and that the repressor at _O_L3 appears to interact specifically with the repressor at _O_R3. The _O_L3-CI-_O_R3 interaction involves the same CI interface used for short-range dimer-dimer interactions and does not occur without the other four operators. The long-range interactions were incorporated into a physicochemical model, allowing estimation of the long-range interaction energies and showing the lysogenic state to be ideally poised for CI negative autoregulation. The results establish the λ system as a powerful tool for examining long-range gene regulatory interactions in vivo.
Footnotes
Article and publication are at http://www.genesdev.org/cgi/doi/10.1101/gad.1167904.
↵3 Corresponding author. E-MAIL ian.dodd{at}adelaide.edu.au; FAX +61-8-8303-4348.
- Accepted December 19, 2003.
- Received November 6, 2003.
Cold Spring Harbor Laboratory Press