Nucleotide sequence and protein products of two new nodulation genes of Rhizobium meliloti, nodP and nodQ.

Previous studies had suggested the existence of nodulation (nod) genes downstream of nodG in Rhizobium meliloti strain 1021. We have established the DNA sequence and analyzed the translation products of the genes located in this position. Computer analysis of the DNA sequence revealed a number of overlapping putative open-reading frames (ORFs), so we constructed several clones that contained either full-length or truncated ORFs. The protein products of these clones were expressed in both R. meliloti and Escherichia coli in vitro transcription-translation systems. These assays unambiguously defined the expressed ORFs, which we named nodP and nodQ. In addition, we found homology to these genes, via Southern hybridizations, elsewhere in the genome of R. meliloti strain 1021, and in other species of Rhizobium. The nodP gene also displayed homology to E. coli. A computer search revealed significant homology between NodQ and the GDP binding domain of elongation factor Tu (EF-Tu).