Isolation and sequencing of a second Rhizobium tropici CFN299 genetic locus that contains genes homologous to amino acid sulphate activation genes

A Rhizobium tropici CFN299 DNA region, homologous to genes involved in Nod factor synthesis and amino acid sulphate activation, was isolated from a ge nome library. DNA sequence analysis revealed two open reading frames, orf1 and orf2. ouf1 showed highest sequence similarity to the Escherichia coli c ysD gene while orf2 is closely related to Rhizobium sp. N33 nodQ. However, the orf2 deduced peptide is 152 amino acids shorter than Rhizobium sp. N33 NodQ, and lacks the 3'-phosphoadenosine 5'-phosphosulfphate-binding motif. A dendrogram based on the alignment of the deduced amino acid sequences of orf2/nodQ/cysN genes separated Escherichia coli cysN and orf2 from the nodQ cluster. Upstream of ouf1, partial sequence analysis revealed the 3' part of an orf that is highly similar to E. coli cysH. The G+C content of orf1 a nd orf2 differs significantly from the G+C content of R. tropici symbiotic sulphate activation nodPQ genes. This data suggests that the isolated R, tr opici CFN299 locus contains housekeeping genes for amino acid sulphate acti vation.