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Distinguishing Characteristics of Hyperrecombinogenic RecA Protein from Pseudomonas aeruginosa Acting in Escherichia coli

Division of Molecular and Radiation Biophysics, Petersburg Nuclear Physics Institute, Russian Academy of Sciences, Gatchina, St. Petersburg 188300, Russia,¹ Research-Education Center Biophysics, St. Petersburg State Polytechnic University, St. Petersburg 194021, Russia,² Department of Biochemistry, University of Wisconsin, 433 Babcock Drive, Madison, Wisconsin 53706-1544³

Received 13 March 2006/ Accepted 9 June 2006

In Escherichia coli, a relatively low frequency of recombination exchanges (FRE) is predetermined by the activity of RecA protein, as modulated by a complex regulatory program involving both autoregulation and other factors. The RecA protein of Pseudomonas aeruginosa (RecA_Pa) exhibits a more robust recombinase activity than its E. coli counterpart (RecA_Ec). Low-level expression of RecA_Pa in E. coli cells results in hyperrecombination (an increase of FRE) even in the presence of RecA_Ec. This genetic effect is supported by the biochemical finding that the RecA_Pa protein is more efficient in filament formation than RecA K72R, a mutant protein with RecA_Ec-like DNA-binding ability. Expression of RecA_Pa also partially suppresses the effects of recF, recO, and recR mutations. In concordance with the latter, RecA_Pa filaments initiate recombination equally from both the 5' and 3' ends. Besides, these filaments exhibit more resistance to disassembly from the 5' ends that makes the ends potentially appropriate for initiation of strand exchange. These comparative genetic and biochemical characteristics reveal that multiple levels are used by bacteria for a programmed regulation of their recombination activities.