Dual regulation of a polyethylene glycol degradative operon by AraC-type and GAlR-type regulators in Sphingopyxis macrogoltabida strain 103

The genes for polyethylene glycol (PEG) catabolism (pegB, C, D, A and E) in Sphingopyxis macrogoltabida strain 103 were shown to form a PEG-inducible operon. The pegR gene, encoding an AraC-type regulator in the downstream area of the operon, is transcribed in the reverse direction. The transcription start sites of the operon were mapped, and three putative σ⁷⁰-type promoter sites were identified in the pegB, pegA and pegR promoters. A promoter activity assay showed that the pegB promoter was induced by PEG and oligomeric ethylene glycols, whereas the pegA and pegR promoters were induced by PEG. Deletion analysis of the pegB promoter indicated that the region containing the activator-binding motif of an AraC/XyIS-type regulator, was required for transcription of the pegBCDAE operon. Gel retardation assays demonstrated the specific binding of PegR to the pegB promoter. Transcriptional fusion studies of pegR with pegA and pegB promoters suggested that PegR regulates the expression of the pegBCDAE operon positively through its binding to the pegB promoter, but PegR does not bind to the pegA promoter. Two specific binding proteins for the pegA promoter were purified and identified as a GaIR-type requlator and an H2A histone fragment (histone-like protein, HU). The binding motif of a GalR/Lacl-type regulator was found in the pegA and pegR promoters. These results suggested the dual regulation of the pegBCDAE operon through the pegB promoter by an AraC-type regulator, PegR (PEG-independent), and through thepegA and pegR promoters by a GaIR/ Lacl-type regulator together with HU (PEG-dependent).