RecA-ssDNA filaments supercoil in the presence of single-stranded DNA-binding protein
- Department of Chemical Engineering, University of Michigan, 3074 H.H. Dow, 2300 Hayward Street, Ann Arbor, MI 48109-2136 (United States)
- Department of Chemical Engineering; University of Michigan; 3074 H.H. Dow; 2300 Hayward Street; Ann Arbor; MI 48109-2136 (United States) and Department of Macromolecular Science and Engineering; University of Michigan; 3074 H.H. Dow; 2300 Hayward Street; Ann Arbor; MI 48109-2136 (United States) and Department of Biomedical Engineering; University of Michigan; 3074 H.H. Dow; 2300 Hayward Street; Ann Arbor; MI 48109-2136 (United States) and Department of Mechanical Engineering; University of Michigan; 3074 H.H. Dow; 2300 Hayward Street; Ann Arbor; MI 48109-2136 (United States)
Using atomic force microscopy (AFM), we find that RecA-single-stranded DNA (RecA-ssDNA) filaments, in the presence of single-stranded DNA-binding (SSB) protein, organize into left-handed bundles, which differ from the previously reported disordered aggregates formed when SSB is excluded from the reaction. In addition, we see both left- and right-handedness on bundles of two filaments. These two-filament supercoils, individual filaments, and other smaller bundles further organize into more complicated bundles, showing overall left-handedness which cannot be explained by earlier arguments that presumed supercoiling is absent in RecA-ssDNA filaments. This novel finding and our previous results regarding supercoiling of RecA-double-stranded DNA (RecA-dsDNA) filaments are, however, consistent with each other and can possibly be explained by the intrinsic tendency of RecA-DNA filaments, in their fully coated form, to order themselves into helical bundles, independent of the DNA inside the filaments (ssDNA or dsDNA). RecA-RecA interactions may dominate the bundling process, while the original conformation of DNA inside filaments and other factors (mechanical properties of filaments, concentration of filaments, and Mg{sup 2+} concentration) could contribute to the variation in the appearance and pitch of supercoils. The tendency of RecA-DNA filaments to form ordered supercoils and their presence during strand exchange suggest a possible biological importance of supercoiled filaments.
- OSTI ID:
- 20991380
- Journal Information:
- Biochemical and Biophysical Research Communications, Journal Name: Biochemical and Biophysical Research Communications Journal Issue: 3 Vol. 357; ISSN 0006-291X; ISSN BBRCA9
- Country of Publication:
- United States
- Language:
- English
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