Single molecule analysis of DNA wrapping and looping by a circular 14mer wheel of the bacteriophage 186 CI repressor

• Type of Material: Article
• Authors: Haowei Wang, Emory University; Ian B. Dodd, University of Adelaide; David Dunlap, Emory University; Keith E. Shearwin, University of Adelaide; Laura Finzi, Emory University
• Language: English
• Date: 2013-04-24
• Publisher: Oxford University Press (OUP): Policy C - Option B
• Publication Version: Final Published Version
• Copyright Statement: © The Author(s) 2013. Published by Oxford University Press.
• License: Creative Commons Attribution-Noncommercial 3.0 Unported
• Final Published Version (URL): http://nar.oxfordjournals.org/content/41/11/5746
• Title of Journal or Parent Work: Nucleic Acids Research
• ISSN: 0305-1048
• Volume: 41
• Issue: 11
• Start Page: 5746
• End Page: 5756
• Grant/Funding Information: Funding for open access charge: NIH (to L.F.) and other (to K.E.S.).; National Institutes of Health (NIH) [RGM084070A to L.F.]; Australian Research Council [DP110100824 to K.E.S., I.B.D. and L.F.].
• Research Categories: Chemistry, Biochemistry; Biology, Cell

Abstract

The lytic–lysogenic decision in bacteriophage 186 is governed by the 186 CI repressor protein in a unique way. The 186 CI is proposed to form a wheel-like oligomer that can mediate either wrapped or looped nucleoprotein complexes to provide the cooperative and competitive interactions needed for regulation. Although consistent with structural, biochemical and gene expression data, many aspects of this model are based on inference. Here, we use atomic force microscopy (AFM) to reveal the various predicted wrapped and looped species, and new ones, for CI regulation of lytic and lysogenic transcription. Automated AFM analysis showed CI particles of the predicted dimensions on the DNA, with CI multimerization favoured by DNA binding. Measurement of the length of the wrapped DNA segments indicated that CI may move on the DNA, wrapping or releasing DNA on either side of the wheel. Tethered particle motion experiments were consistent with wrapping and looping of DNA by CI in solution, where in contrast to λ repressor, the looped species were exceptionally stable. The CI regulatory system provides an intriguing comparison with that of nucleosomes, which share the ability to wrap and release similar sized segments of DNA.