AUTOREGULATION AND KINETICS OF INDUCTION OF THE RHIZOBIUM-PHASEOLI RECA GENE

A fusion between the recA gene of Rhizobium phaseoli and the lacZ gene was constructed in vitro and cloned in a mini-Tn5 transposon derivati ve to obtain chromosomal insertions which make it possible to quantita tively examine their transcriptional regulation in both R. phaseoli an d E. coli. Likewise, and by insertion of a spectinomycin-resistance ge ne cassette into the recA gene of R. phaseoli and subsequent marker ex change, a RecA(-) derivative of this bacterial species has been obtain ed. Analysis of this recA-lacZ fusion showed that it was inducible by DNA damage in the RecA(+) strain of R. phaseoli but not in the RecA(-) mutant. On the other hand, the recA-lacZ fusion of R. phaseoli was no t induced in DNA-damaged RecA(+) cells of E. coli. Furthermore, the ra nge of UV doses which give rise to dose dependence in the induction of its respective recA genes is different in R. phaseoli from that in E. coli.