Nature Structural & Molecular Biology11, 936 - 944 (2004)
Published online: 7 September 2004; | doi:10.1038/nsmb823
Intron-encoded homing endonuclease I-TevI also functions as a transcriptional autorepressor
David R Edgell1, 3, Victoria Derbyshire1, Patrick Van Roey1, Stephen LaBonne2, 3, Matthew J Stanger1, Zhong Li1, Thomas M Boyd2, 3, David A Shub2
& Marlene Belfort1
1
Wadsworth Center, New York State Department of Health, Center for Medical Sciences, 150 New Scotland Avenue, Albany, New York 12208, USA.
2
Department of Biological Sciences, University at Albany-SUNY, 1400 Washington Avenue, Albany, New York 12222, USA.
3
Present addresses: Department of Biochemistry, Medical Sciences Building, University of Western Ontario, London, Ontario N6A 5C1, Canada (D.R.E.), Lake County Crime Laboratory, 235 Fairgrounds Road, Painesville, Ohio 44077, USA (S.L.) and Department of Emergency Medicine, Jacobi Medical Center, 1400 Pelham Parkway, Bronx, New York 10461, USA (T.M.B.).
Customary binding sites of intron-encoded homing endonucleases lie within cognate intronless alleles, at the so-called homing sites. Here, we describe a novel, high-affinity binding site for I-TevI endonuclease, encoded within the group I td intron of phage T4. This site is an operator that overlaps the T4 late promoter, which drives I-TevI expression from within the td intron. I-TevI binds the operator and homing sites with equal affinity, and functions as a transcriptional autorepressor. Distinct sequence and spacing requirements of the catalytic domain result in reduced cleavage activity on operator DNA. Crystallographic studies showed that the overall interactions of the DNA-binding domain with the operator and homing sites are similar, but have some different hydrogen-bonding contacts. We present a model in which the flexibility in protein-DNA interactions allows I-TevI to bind variant intronless alleles to promote intron mobility while facilitating its function in autorepression, and thereby persistence in its host.
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