Characterization of a halobacterial gene affecting bacterio-opsin gene expression

Abstract

A substantial number of spontaneous bacterio-opsin mutants of Halobacterium halobium are the result of insertion elements up to 1400 bp upstream of the bacterio-opsin (bop) gene. The nucleotide sequence of 1800 bp upstream of the bop gene has been determined. There is a 1118 bp open reading frame (ORF) located within this region which is transcribed and which coincides with the distribution of insertion elements upstream of the bop gene in Bop mutants. Therefore, we propose that there is a gene (brp gene) 526 bp upstream of the bop gene. This putative gene is transcribed in the opposite direction as the bop gene and could encode a protein of 37,500 D (359 amino acids) with a codon usage similar to bacterio-opsin. The 5' terminus of the brp transcript has been determined. The brp transcript and the bop mRNA are complementary for 13 residues near their 5' termini and both transcripts start at or near the initiating codon of the gene. Both transcripts could form similar hairpin loop structures at their 5' termini which contain possible ribosomal binding sites. The DNA sequences immediately upstream of the bop and the brp genes have significant homologies and there is a short complementary sequence. The role of the brp gene in bacterio-opsin gene expression is unclear.

brp and blh Are Required for Synthesis of the Retinal Cofactor of Bacteriorhodopsin in Halobacterium salinarum

“…2, inset, lane 2), indicating that the loss of BR was attributable to the absence of BO. These results are consistent with the earlier findings that insertions in brp abolish BR and bop mRNA production (15,16,21). As acknowledged previously (21), insertions in brp may prematurely abort an mRNA transcript that encodes both Brp and Bat, thereby reducing bat transcription and preventing bop transcriptional activation.…”

“…However, cellular factors may be required to prevent the photooxidation or photoisomerization of the cofactor during its transport or binding to BO. These functions may be mediated by a retinal-specific chaperone or by a multifunctional enzyme that converts ␤-carotene to retinal and transports or binds retinal to BO.As a first step to identify cellular factors that mediate these processes, we chose to study the brp gene, which encodes a putative membrane protein (Brp) implicated in BR biogenesis (15)(16)(17)(18). The brp gene is part of a gene cluster (Fig.…”

“…As a first step to identify cellular factors that mediate these processes, we chose to study the brp gene, which encodes a putative membrane protein (Brp) implicated in BR biogenesis (15)(16)(17)(18). The brp gene is part of a gene cluster (Fig.…”

“…1) that includes bop, which encodes BO; bat, which encodes a transacting factor (Bat) that contains a region homologous to the PAS domain of the oxygen sensor NifL (19,20) and activates bop expression under microaerobic conditions (21,22); and blp, a gene of unknown function (23). Insertions in brp greatly decrease BR and bop mRNA levels (15)(16)(17)(18). This result can be interpreted to imply that Brp modulates bop expression (18,21).…”

The nucleotide sequence of the genes coding for the S19 and L22 equivalent ribosomal proteins from Halobacterium halobium

“…In the halophilic branch of archaebacteria, the primary structures of a number of stable RNA genes from different species are now available [2][3][4][5]. However, only a few protein genes from halobacteria have been sequenced [6][7][8][9]. Thus, the investigation of other halobacterial sequences could illuminate the peculiarities of gene expression.…”