SUNY at Albany
June 19-23, 2001
Morphological Aspects of the SOS Response
The inducible SOS response increases the ability of bacteria to cope with DNA damage through various DNA repair processes in which the RecA protein plays a central role. We present the first study of the morphological aspects that accompany the SOS response in E. coli. By using cryo-electron-microscopy techniques we show that induction of the SOS system in wild-type bacteria results in a fast and massive intracellular coaggregation of RecA and DNA into a lateral macroscopic assembly. The coaggregates comprise substantial portions of both the cellular RecA and the DNA complement. As DNA damages accumulate, the assembly becomes crystalline. The structural features of the coaggregates and their relation to in-vitro RecA-DNA networks, as well as morphological studies of strains carrying RecA mutants, are all consistent with the possibility that the intracellular assemblies represent a functional entity in which RecA-mediated DNA repair and protection activities occur. Specifically, we propose that the lateral organization facilitates the RecA-mediated search for DNA homology. We further suggest that the crystalline order that is progressively assumed by the assembly allows for RecA-related DNA protection through physical sequestration.
S. Levin-Zaidman, D. Frenkiel-Krispin, E. Shimoni, S. G. Wolf and A. Minsky*
Department of Organic Chemistry
The Weizmann Institute of Science
Rehovot 76100, Israel