Using a neural network promoter prediction tool [28], we predicted a putative transcriptional start site (P2) adjacent to the area containing a ChvI binding site (B). Another putative transcriptional start site (P1) further upstream from SMb21188 suggests that transcription might be directed from two differently regulated promoters, only one of which would include the SMb21188 gene. Figure 2 Transcriptional fusion assays and the msbA2 operon. (A) GusA activities were measured DMXAA cost for fusions in genes

SMb21189, SMb21190, and msbA2 in wild-type (Rm1021) and chvI261 mutant (SmUW38) click here strain backgrounds. No GusA activities above background levels were detected for fusions to SMb21189 and SMb21190 in the chvI261 mutant strain background. (B) In the operon diagram, F1, F2, and F3 represent the positions

of the fusions to SMb21189, SMb21190 and msbA2 respectively. The grey box (B) represents the region for ChvI binding, and P1 and P2 are predicted promoters. Reporter gene fusion assays and promoter prediction were done with fusions in genes SMc00262 and SMc00261, which are IWP-2 nmr predicted to encode a 3-ketoacyl-CoA thiolase and a fatty-acid-CoA ligase respectively (Figure 3B). In this case, a promoter was predicted immediately upstream of the ChvI binding area in SMc00262 and accordingly the fusions further downstream in SMc00262 and in SMc00261 presented higher expression levels in chvI mutant strains than in wild type (Figure 3A). These results suggest that ChvI Amino acid acts by repressing the transcription of the SMc00264 – SMc00259 operon. Figure 3 Transcriptional fusion assays and the SMc00261 operon. (A) GusA activities were measured for fusions in genes SMc00262 and SMc00261 in wild-type (Rm1021)

and chvI261 mutant (SmUW38) strain backgrounds. (B) In the operon diagram, F1 and F2 represent the position of the fusions to SMc00262 and SMc00261 respectively. The grey box (B) represents the region for ChvI binding, and P1, P2 and P3 are predicted promoters. S. meliloti produces an iron-siderophore, rhizobactin 1021, under iron-depleted conditions [29]. Genes for the synthesis and transport of rhizobactin are clustered in an operon [30]. The rhizobactin transporter coding sequence (rhtX, SMa2337) was found to contain two DNA fragments binding ChvI (Table 1 and Figure 4B). We tested a fusion following the first binding site (B1) and two other fusions further in rhbB (SMa2402; diaminobutyrate decarboxylase, EC 4.1.1.86) and in rhbF (SMa2410). The promoter prediction suggests the presence of a promoter before rhtX and another one before rhbA. The β-glucuronidase assays presented a higher expression in chvI background for all three fusions. This suggests that ChvI represses the expression of genes required for the synthesis and transport of rhizobactin 1021.