The LacI Family Protein GlyR3 Co-regulates the Operon and in

Background: utilizes a wide variety of free and cellulosomal cellulases and accessory enzymes to hydrolyze polysaccharides present in complex substrates. To date only a few studies have unveiled the details by which the expression of these cellulases are regulated. Recent studies have described the auto regulation of the operon and determined that the -- gene cluster and nearby - gene cluster are co-transcribed as polycistronic mRNA.

Results: In this paper, we demonstrate that the GlyR3 protein mediates the regulation of We first identify putative GlyR3 binding sites within or just upstream of the coding regions of and . Using an electrophoretic mobility shift assay (EMSA), we determined that a higher concentration of GlyR3 is required to effectively bind to the putative site in comparison to the site. Neither the putative site nor random DNA significantly binds GlyR3. While laminaribiose interfered with GlyR3 binding to the binding site, binding to the site was unaffected. In the presence of laminaribiose, in vivo transcription of the -- gene cluster increases, while expression is repressed, compared to in the absence of laminaribiose, consistent with the results from the EMSA. An in vitro transcription assay demonstrated that GlyR3 and laminaribiose interactions were responsible for the observed patters of in vivo transcription.

Conclusions: Together these results reveal a mechanism by which is expressed at low concentrations of GlyR3 but repressed at high concentrations. In this way, is able to co-regulate both the and gene clusters in response to the availability of β-1,3-polysaccharides in its environment.