LOCATIONS OF FUNCTIONAL DOMAINS IN THE RECA PROTEIN - OVERLAP OF DOMAINS AND REGULATION OF ACTIVITIES

`We review the locations of various functional domains of the RecA pro tein of Escherichia coli, including how they have been assigned, and d iscuss the potential regulatory roles of spatial overlap between diffe rent domains. RecA is a multifunctional and ubiquitous protein involve d both in general genetic recombination and in DNA repair: it regulate s the synthesis and activity of DNA repair enzymes (SOS induction) and catalyses homologous recombination and mutagenesis. For these activit ies RecA interacts with a nucleotide cofactor. single-stranded and dou ble-stranded DNAs, the LexA repressor, UmuD protein, the UmuD(2)'C com plex as well as with RecA itself in forming the catalytically active n ucleofilament. Attempts to locate the respective interaction sites hav e been advanced in order to understand the various functions of RecA. An intriguing question is how these numerous functional sites an conta ined within this rather small protein (38 kDa). To assess more clearly the roles of the respective sites and to what extent the sites may be interacting with each other, we review and compare the results obtain ed from various biological, biochemical and physico-chemical approache s. From a three-dimensional model it is concluded that all sites are c oncentrated to one part of the protein. As a consequence there are sig nificant overlaps between the sites and it is speculated that correspo nding interactions may play important roles in regulating RecA activit ies.