LasX, a transcriptional regulator of the lactocin S biosynthetic genes in Lactobacillus sakei L45, acts both as an activator and a repressor
2002
Andersen Rawlinson, E.L. ((Agricultural University of Norway, Aas (Norvège). Laboratory of Microbial Gene Technology)) | Nes, I.F. | Skaugen, M.
The 11 kb las locus, present on the 50 kb plasmid pCIM1 , specifies the production of the lantibiotic lactocin S in Lactobacillus sakei L45. The gene cluster is organized into two oppositely orientated operons, lasAMNTUVPJW (lasA-W) and lasXY, the former of which contains the biosynthetic, immunity and transport genes. We have previously shown that inactivation of lasX abolishes lactocin S production and causes a drastic reduction in lasA-specific transcripts (encoding pre-lactocin S). The aim of this study was to determine whether or not the product of lasX, which is significantly similar to Rgg-like regulators, was directly involved in transcriptional regulation of the lactocin S biosynthetic genes. The divergently orientated and overlapping promoters, PlasA-W --gusA and PlasXY, were transcriptionally fused to the Escherichia coli gusA gene, and the activity of the fusions was assayed in the presence and absence of lasX, which was expressed on a separate plasmid. A significant stimulation of expression (5-6-fold) of the PlasA-W-gusA fusion was observed in the presence of lasX, whereas expression of the PlasXY-gusA construct was reduced 1.5-2-fold. Our results strongly suggest that LasX is a bifunctional regulatory protein, acting both as an activator of lasA-W transcription and as a repressor of lasXY transcription. While a transcription stimulation activity has been described for several of the Rgg-like proteins, the present study is the first to report an autorepressor function for a member of this protein group
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