Discussion In contrast to what has been observed in E. coli and Pseudomonas putida , the PA genes of B. cenocepacia K56-2 are organized into three gene clusters. We
hypothesize that this arrangement may allow regulation of gene expression at different levels. The observation that eGFP expression driven by P paaA is roughly 3-fold stronger than either the P paaH or P paaZ promoters (Figure 1) is suggestive of a higher requirement for the product of the PaaABCDE enzymatic complex than the other intermediates. This could be simply due to the optimal PRIMA-1MET research buy kinetic coupling between the different steps or that the product of the ring hydroxylation complex is used in a second pathway with a yet unknown selleck screening library biological function. The presence of a poly(A) tract upstream of the paaA -35 element (Figure 5A) that resembles an UP element  may likely account for the increased activity. Our results also show that BCAL0210 is necessary for repression of PA dependent activity of the paaA, paaH and paaZ gene promoters (Figure 1). Therefore, BCAL0210
(PaaR) encoding for a TetR-type transcriptional regulator is involved in negative regulation of the PA catabolic genes. Since a conserved inverted repeat DNA sequence is necessary for PA negative control of paaA gene expression (Table 2), we hypothesize that BCAL0210 binds the IRs VX-661 located in the core promoter of the paaA, paaZ and paaH genes to negatively regulate transcription of the PA catabolic genes. It should be noted however, that the insertional mutagenesis
system used to produce JNRH1 introduces polar mutations . Although the possibility of polar effects on genes downstream BCAL0210 cannot be ruled out, the downstream gene BCAL0209, encoding a putative GNAT family acetyl transferase located several hundred base pairs downstream of BCAL0211 makes the possibility of polar effects unlikely. On the other hand, BCAL0211 and BCAL0210 are located on the same transcript (Figure 4) and thus are co-regulated at the transcriptional level. TetR-type proteins are known Selleck Erastin to regulate their own transcription by self-repression . Currently it is unknown if the conserved IR located in the DNA leader sequence of the BCAL0211 gene may be involved in regulation of this gene cluster. Whether BCAL0211, which encodes for a protein of unknown function (DUF1835) is involved in some fashion in the regulation of the PA genes remains to be determined. Table 2 Activity of PpaaA and IR mutated derivatives as a result of growth in M9 minimal media containing glycerol or PA. Strain/plasmid Mean fluorescence/O.D.600 ± SD with indicated carbon sources Gly PA K56-2/pJH7 187 ± 33 1096 ± 107 K56-2/pJH10 1579 ± 10 1062 ± 15 K56-2/pJH11 1345 ± 111 1026 ± 52 K56-2/pJH12 2159 ± 111 1503 ± 60 B. cenocepacia K56-2 containing eGFP translational reporters P paaA were grown for 18 hours in M9 minimal media supplemented with glycerol or PA.