A small basic protein from the brz-brb operon is involved in regulation of bop transcription in Halobacterium...

The halophilic archaeon Halobacterium salinarum expresses bacteriorhodopsin, a retinal-protein that allows photosynthetic growth. Transcription of the bop (bacterioopsin) gene is controlled by two transcription factors, Bat and Brz that induce bop when cells are grown anaerobically and under light.

A new gene was identified that is transcribed together with the brz gene that encodes a small basic protein designated as Brb (bacteriorhodopsin-regulating basic protein). The translation activity of the start codon of the brb gene was confirmed by BgaH reporter assays. In vivo site-directed mutagenesis of the brb gene showed that the Brb protein cooperates with Brz in the regulation of bop expression. Using a GFP reporter assay, it was demonstrated that Brb cooperates with both Brz and Bat proteins to activate bop transcription under phototrophic growth conditions.

The activation of the bop promoter was shown to be dependent not only on two major factors, Bat and Brz, but is also tuned by the small basic protein, Brb.