MUTATIONAL ANALYSIS OF THE RHIZOBIUM-ETLI RECA OPERATOR

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