Complementation of the mutant phenotype by the asnO gene. RNAs isolated from free-living microoxic cultures (2% O2) of S. meliloti strains grown in M9 minimal medium were amplified by RT-PCR using specific primers. RT-PCR products were separated on agarose gels, blotted onto a nylon membrane and hybridized with the 32P labelled probe of the expected product. Upper panel : fixK gene (see Materials and Methods). Lower panel : hemA gene (control). Lane 1 = GMI211 (pMF10), Lane 2 = GMI401 (pMF10), Lanes 3 and 4 = GMI401 (pMF10) (pBasn2) of two independent transconjugants.