Using the technique of Mu dl(Ap lac)-directed lacZ operon fusions, several oxygen-regulated genetic loci were identified in SalmoneUa typhimurum. Thirteen anaerobically inducible and six aerobically inducible operon fusions were identified. Based on control by the oxrA and oxrB regulatory loci, the ani-lacZ fusions were grouped into three classes: class I loci were regulated by both oxr loci, class H genes were regulated by oxrA only, and class m loci were not affected by either regulatory locus. Several of the ani-lacZ fusions required growth in complex medium before they exhibited the inducible phenotype. While the expression of some of these loci was repressed when organisms were grown in nitrate, others were stimulated by nitrate. Fusions into the hyd and phs loci were identified among the Isolated ani-lacZ fusions. Six oxygen-inducible (oxi) operon fusions were also identified. Two of the oxi loci mapped near oxygen-regulatory loci: oxiC near oxrA and oxiE near oxyR. However, neither fusion appeared to occur within the regulatory locus. The data presented serve to further define the aerobic and anaerobic stimulons of S. typhimurium but indicate additional regulatory circuits above those already defined.

The nadR locus (99 min) controls the transcription of several genes involved with either the biosynthesis (nadAB) or recycling (pncB) of NAD in Salmonella typhimurium. Point mutations in this locus were found to cause defects either in the transport of nicotinamide mononucleotide (PnuA-), the regulation of nadAB (NadR-) or both transport and regulation (PnuA-NadR-). Deletions or insertions into nadR always resulted in the PnuA- NadR- phenotypes. Merodiploids constructed with various combinations of PnuA-, NadR- or PnuA- NadR- strains indicate a single complementation group. The results suggest the NadR product is a bifunctional regulatory protein. Operon fusions to lacZ (nadR :: Mud1-8) were used to show that nadR is not autoregulated and is transcribed in a clockwise direction. The gene was also cloned and located within a 2 kb EcoR1-Bg/II fragment.

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