Cloning and mutagenesis of the Rhizobium meliloti isocitrate dehydrogenase gene.
The gene encoding Rhizobium meliloti isocitrate dehydrogenase (ICD) was cloned by complementation of an Escherichia coli icd mutant with an R. meliloti genomic library constructed in pUC18. The complementing DNA was located on a 4.4-kb BamHI fragment. It encoded an ICD that had the same mobility as R. meliloti ICD in nondenaturing polyacrylamide gels. In Western immunoblot analysis, antibodies raised against this protein reacted with R. meliloti ICD but not with E. coli ICD. The complementing DNA fragment was mutated with transposon Tn5 and then exchanged for the wild-type allele by recombination by a novel method that employed the Bacillus subtilis levansucrase gene. No ICD activity was found in the two R. meliloti icd::Tn5 mutants isolated, and the mutants were also found to be glutamate auxotrophs. The mutants formed nodules, but they were completely ineffective. Faster-growing pseudorevertants were isolated from cultures of both R. meliloti icd::Tn5 mutants. In addition to lacking all ICD activity, the pseudorevertants also lacked citrate synthase activity. Nodule formation by these mutants was severely affected, and inoculated plants had only callus structures or small spherical structures.
McDermott
T R
TR
Institute of Biological Chemistry, Washington State University, Pullman 99164-6340.
Kahn
M L
ML
D015153:Blotting, Western; D003001:Cloning, Molecular; D004251:DNA Transposable Elements / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D007521:Isocitrate Dehydrogenase / Q000235:genetics*; D016296:Mutagenesis / Q000235:genetics; D010944:Plants / Q000382:microbiology; D010957:Plasmids / Q000235:genetics; D015183:Restriction Mapping; D016962:Sinorhizobium meliloti / Q000201:enzymology* / Q000235:genetics
D004251:DNA Transposable Elements; D007521:Isocitrate Dehydrogenase