Searching for Homology by Filaments of RecA-like Proteins

The recombinase proteins of the RecA family perform tasks that are essential for cell survival and for the maintenance of genetic diversity. They are able to rearrange genes in new combinations and to repair DNA double-strand breaks in an almost error-free fashion. Their function in homologous recombination is performed in an original way that has no equivalent in the DNA processing machinery: They form long helical filaments on a target DNA, capable of recognizing homologous DNA sequences in the genome and of exchanging DNA strands. How the DNA sequences are recognized during this process and how the DNA strands are exchanged remain matters of investigation. This chapter reviews the information that has been accumulated on recognition and strand exchange, together with the models that aim at organizing this data, viewed at different levels: that of the nucleus, the molecule, or the atom. Altogether, a picture begins to emerge on a multiscale dimension, which presents the search for homology as a complex process with important dynamic components.