Mutational Analysis of the Rhizobium etli recA Operator

Based upon our earlier studies (A. Tapias, A. R. Fernández de Henestrosa, and J. Barbé, J. Bacteriol. 179:1573–1579, 1997) we hypothesized that the regulatory sequence of the Rhizobium etli recA gene was TTGN(11)CAA. However, further detailed analysis of the R. etli recA operator described in the present work suggests that it may in fact be GAACN(7)GTAC. This new conclusion is based upon PCR mutagenesis analysis carried out in the R. etli recA operator, which indicates that the GAAC and GTAC submotifs found in the sequence GAACN(7)GTAC are required for the maximal stimulation of in vivo transcription and in vitro DNA-protein complex formation. This DNA-protein complex is also detected when the GAACN(7)GTAC wild-type sequence is modified to obtain GAACN(7)GAAC, GTACN(7)GTAC, or GAACN(7)GTTC. The wild-type promoters of the Rhizobium meliloti and Agrobacterium tumefaciens recA genes, which also contain the GAACN(7)GTAC sequence, compete with the R. etli recA promoter for the DNA-protein complex formation but not with mutant derivatives in any of these motifs, indicating that the R. etli, R. meliloti, and A. tumefaciens recA genes present the same regulatory sequence.