CHARACTERIZATION OF THE PROMOTER OF THE RHIZOBIUM-ETLI RECA GENE

The promoter of the Rhizobium etli recA gene has been identified by pr imer extension and by making deletions affecting several regions locat ed upstream of its coding region. A gel mobility shift assay carried o ut with crude extracts of cells of R. etli has been used to show that a DNA-protein complex is formed in the R. etli recA promoter region in vitro. Analysis of the minimal region of the recA promoter giving ris e to this DNA-protein complex revealed the presence of an imperfect pa lindrome corresponding to the sequence TTGN(11)CAA. Site-directed muta tion of both halves of this palindrome indicated that both motifs, TTG and CAA, are necessary for both normal DNA-protein complex formation in vitro and full DNA damage-mediated inducibility of the recA gene in vivo. However, the TTG motif seems to be more dispensable than the CA A one. The presence of this same palindrome upstream of the recA genes of Rhizobium meliloti and Agrobacterium tumefaciens, whose expression is also regulated in R. etli cells, suggests that this TTGN(11)CAA se quence may be the SOS box of at least these three members of the Rhizo biaceae.