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Helical Filaments of Human Dmc1 Protein on Single-Stranded DNA: A Cautionary Tale
- Source :
- Journal of Molecular Biology. 401:544-551
- Publication Year :
- 2010
- Publisher :
- Elsevier BV, 2010.
-
Abstract
- Proteins in the RecA/Rad51/RadA family form nucleoprotein filaments on DNA that catalyze a strand exchange reaction as part of homologous genetic recombination. Because of the centrality of this system to many aspects of DNA repair, the generation of genetic diversity, and cancer when this system fails or is not properly regulated, these filaments have been the object of many biochemical and biophysical studies. A recent paper has argued that the human Dmc1 protein, a meiotic homolog of bacterial RecA and human Rad51, forms filaments on single-stranded DNA with approximately 9 subunits per turn in contrast to the filaments formed on double-stranded DNA with approximately 6.4 subunits per turn and that the stoichiometry of DNA binding is different between these two filaments. We show using scanning transmission electron microscopy that the Dmc1 filament formed on single-stranded DNA has a mass per unit length expected from approximately 6.5 subunits per turn. More generally, we show how ambiguities in helical symmetry determination can generate incorrect solutions and why one sometimes must use other techniques, such as biochemistry, metal shadowing, or scanning transmission electron microscopy, to resolve these ambiguities. While three-dimensional reconstruction of helical filaments from EM images is a powerful tool, the intrinsic ambiguities that may be present with limited resolution are not sufficiently appreciated.
- Subjects :
- Microscopy, Electron, Scanning Transmission
Protein Conformation
DNA repair
RAD51
DNA, Single-Stranded
Cell Cycle Proteins
macromolecular substances
Biology
Genetic recombination
DNA-binding protein
Article
DNA-Binding Proteins
Protein filament
Crystallography
chemistry.chemical_compound
Protein structure
chemistry
Structural Biology
Biophysics
Humans
DMC1
Molecular Biology
DNA
Protein Binding
Subjects
Details
- ISSN :
- 00222836
- Volume :
- 401
- Database :
- OpenAIRE
- Journal :
- Journal of Molecular Biology
- Accession number :
- edsair.doi.dedup.....b48528fa3c9348fef3368e24ea745a56