RELATING BIOCHEMISTRY TO BIOLOGY - HOW THE RECOMBINATIONAL REPAIR FUNCTION OF RECA PROTEIN IS MANIFESTED IN ITS MOLECULAR-PROPERTIES

The multiple activities of the RecA protein in DNA metabolism have ins pired over a decade of research in dozens of laboratories around the w orld. This effort has nevertheless failed to yield an understanding of the mechanism of several RecA protein-mediated processes, the DNA str and exchange reactions prominent among them. The major factors impedin g progress are the invalid constraints placed upon the problem by atte mpting to understand RecA protein-mediated DNA strand exchange within the context of an inappropriate biological paradigm - namely, homologo us genetic recombination as a mechanism for generating genetic diversi ty. In this essay I summarize genetic and biochemical data demonstrati ng that RecA protein evolved as the central component of a recombinati onal DNA repair system, with the generation of genetic diversity being a sometimes useful byproduct, and review the major in vitro activitie s of RecA protein from a repair perspective. While models proposed for both recombination and recombinational repair often make use of DNA s trand cleavage and transfer steps that appear to be quite similar, the molecular and thermodynamic requirements of the two processes are ver y different. The recombinational repair function provides a much more logical and informative framework for thinking about the biochemical p roperties of RecA and the strand exchange reactions it facilitates.