SUMMARY: is able to utilize -arginine as the energy source for growth under anaerobic, nitrate-free conditions. Mutations in the chromosomal gene cluster specifying the inducible arginine deiminase pathway enzymes abolish fermentative growth on arginine. From two different ::Tn 5-751 insertion mutants of recombinant plasmids have been derived which carry a resistance marker of transposon Tn plus flanking parts of the region. These recombinant plasmids served to reconstruct the functional cluster on a 5.6 kb fragment, which was inserted into the broad-host-range vector pKT240. In this 5.6 kb segment complemented mutations in and contained the control region necessary in for enzyme induction by oxygen limitation and arginine. The results of subcloning experiments and transcriptional fusions, the polarity of transposon insertions and the effect of external promoters led to the conclusion that the structural genes (for arginine deiminase), (for catabolic ornithine carbamoyltransferase) and (for carbamate kinase) are contiguous and transcribed in the same direction. Thus, the cluster appears to have the characteristics of an operon. In the cloned genes were expressed at low, non-inducible levels; strong vector promoters enhanced expression up to 100-fold. This indicates that transcriptional initiation at the promoter(s) is poor in


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