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 derivative to obtain chromosomal insertions which make it possible to quantitatively examine their transcriptional regulation in both R. phaseoli and E. coli. Likewise, and by insertion of a spectinomycin-resistance gene cassette into the recA gene of R. phaseoli and subsequent marker exchange, a RecA(-) derivative of this bacterial species has been obtained. 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 not induced in DNA-damaged RecA(+) cells of E. coli. Furthermore, the range 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.