Albany 2001

category image Biomolecular
SUNY at Albany
June 19-23, 2001

Superfamily of RecA-like Proteins Active in DNA Recombination and Replication

RecA-like proteins exist in all kingdoms of life, and are involved in the recombination and repair of DNA. All of these proteins polymerize on DNA to produce long helical nucleoprotein complexes. Within these complexes, the DNA is found to be in a very similar conformation, with an extension to ~ .5 nm per base pair (extended by about 50% from B-form), and unwound from ~ 10 bp/turn to ~ 19 bp/turn. Thus, the helical pitch of the DNA is ~ 9.5 nm, which, not coincidentally, is the helical pitch of the protein filaments. The use of a novel method for image analysis of helical polymers (1) has given us many new insights into the structural details of these filaments formed by proteins from eubacteria, bacteriophage, archaea, yeast and humans. All of these proteins contain a common nucleotide-binding core, with additional domains that have no sequence or structural homology added to this common core. We suggest that the N-terminal domain of the yeast and human Rad51 filament may have emerged to play a similar role as the C-terminal domain of the bacterial RecA protein by a process of convergent evolution. Detailed analysis of the helical parameters of these filaments suggests that an underlying DNA may be providing coupling over evolution between differences in pitch and twist. In this possibility, the proteins are stabilizing an existing state of DNA. Thus, several aspects of these filaments may have arisen from convergent evolution, including the maintenance of this highly unusual DNA structure. All of these filaments contain the same nucleotide-binding core found in helicases (2), many of which function as hexameric rings. Proteins from the RecA-family can also bind DNA as ring structures (3), and the archaeal RadA protein (a RecA homolog), which binds DNA as both a helical filament and an octameric ring, may provide insight into the functional divergence between the rings and filaments.

References and Footnotes
  1. Egelman, E.H. (2000). "A Robust Algorithm for the Reconstruction of Helical Filaments Using Single-Particle Methods." Ultramicroscopy 85, 225-234.
  2. Bird, L.E., Subramanya, H.S., Wigley, D.B.(1998). "Helicases: a unifying structural theme?" Curr. Opin. Struct. Biol. 8:14-8.

Xiong Yu, Margaret VanLoock, Shixin Yang, Edward H. Egelman

Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences Center, Charlottesville, VA 22908-0733
Phone: 804-924-8210; Fax: 804-924-5069; email: egelman@virginia.edu