RHIZOBIUM-MELILOTI HOMOLOGS OF ESCHERICHIA-COLI MUR GENES

The pectate-lyase-encoding gene pelB of Erwinia chrysanthemi Ec16 was used as a probe for hybridization to Rhizobium meliloti Rm1021 chromos omal DNA under low-stringency conditions. An Rm1021 DNA fragment that hybridized to this probe was cloned and sequenced. Results of RNA hybr idization indicate that a portion of the cloned fragment is transcribe d in R. meliloti. Although the Rm1021 fragment shares no significant n ucleotide sequence identity with Ec16 pelB, it includes an ORF (open r eading frame) that shares a high degree of nt sequence identity with t he Escherichia coli murD gene. This gene codes for UDP-N-acetylmuramoy l-L-alanyl-D-glutamate synthetase, which catalyzes a step in the synth esis of the E. coli cell wall. The R. meliloti putative murD sequence is preceded by a partial ORF that shares sequence identity with mraY. The orientation of the two ORFs in R. meliloti is similar to that of t he E. coli murD and mraY genes.