Identification of a bacterio-opsin species with a N-terminally extended amino acid sequence

In vitro synthesis of bacterio-opsin: integration into microsomal membranes

The translation and membrane integration of bacterio-opsin from Halobacterium salinarium were investigated. Plasmids containing the bacterio-opsin-gene with or without its original presequence were transcribed with the T7-RNA-polymerase and translated in vitro in a wheat germ system. The integration of the expressed bacterio-opsin into dog pancreas microsomes was studied. Both precursor bacterio-opsin and mature bacterio-opsin integrate into the eukaryotic membrane.

Association of the halobacterial 7S RNA to the polysome correlates with expression of the membrane protein bacterioopsin

The sedimentation behavior of the halobacterial 7S RNA and bacterioopsin mRNA was assessed after application of total cell lysates to sucrose gradients. These two RNAs cosedimented predominantly with membrane-bound polysomes, and the quantity of 7S RNA bound to the ribosomes was directly correlated with the expression of bacterioopsin. Puromycin treatment released the 7S RNA from the polysomes, indicating that it is transiently associated with protein translation. We suggest that halobacteria contain a signal-recognition-like particle involved in translation of membrane-associated proteins.

A gene in the archaebacterium Sulfolobus solfataricus that codes for a protein equivalent to the alpha subunits of the signal recognition particle receptor in eukaryotes

We have sequenced a gene in the archaebacterium Sulfolobus solfataricus that codes for a protein that shows sequence similarity to the alpha subunit of the signal recognition particle receptor or docking protein in eukaryotes and the product of the ftsY gene in Escherichia coli. Comparison of the Sulfolobus 'docking protein' with its eukaryotic and eubacterial counterparts showed that the region of highest sequence similarity corresponds to a GTP-binding site. The presence of this gene in archaebacteria suggests that some of the components involved in protein transport have been conserved in the three kingdoms.

Bacteriorhodopsin precursor is processed in two steps

Besides the Coomassie-blue-stained band corresponding to mature bacterioopsin two additional bands of slightly higher apparent molecular masses were observed in purple membrane preparations from Halobacterium halobium by SDS-PAGE. The staining intensity within the triple band pattern varied with the age of the cell culture. For cells in the stationary growth phase the lower band, corresponding to mature bacterioopsin, is the predominant one. Immunodetection and site-specific proteolysis with papain identified the upper band as originating from the previously described precursor of bacterioopsin with its 13-amino-acid-long N-terminal presequence. Our results suggest that the intermediate band is due to a modified precursor of bacterioopsin with a truncated presequence of about eight amino acids. A two-step mechanism for the processing of pre-bacterioopsin to the mature protein in this archaebacterium is proposed.

The opsin family of proteins

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Complete nucleotide sequence and identification of membrane components of the histidine transport operon of S. typhimurium

The nucleotide sequence of the entire histidine transport operon from Salmonella typhimurium has been determined and is shown to consist of four genes, hisJ, hisQ, hisM and hisP. This operon provides the only example of a binding protein-dependent transport system for which the total number of protein components is known. Determination of the amino acid compositions and sequences of these four transport proteins, together with analysis of various transport mutants, allows us to propose a molecular model for binding protein-dependent transport.

Bacteriorhodopsin: partial sequence of mRNA provides amino acid sequence in the precursor region

mRNA for bacteriorhodopsin from Halobacterium halobium has been partially purified. By using this mRNA as template in the presence of reverse transcriptase RNA-dependent DNA nucleotidyltransferase and a 5'-[32P] synthetic oligodeoxyribonucleotide corresponding to amino acids 9-12 of bacteriorhodopsin as primer, we have isolated the major 5'-[32P]cDNA product, approximately 80 nucleotides long, and determined its sequence. Based on the cDNA sequence, the 5'-proximal sequence of bacteriorhodopsin mRNA is G-C-A-U-G-U-U-G-G-A-G-U-U-A-U-U-G-C-C-A-A-C-A-G-C-A-G-U-G-G-A-G-G-G-G-G-U-A-U-C -G-C-A-G-G-C-C-C-A-G-A-U-C-A-C-C-G-G-A-C-G-U-C-C-G. This includes the expected sequence for amino acids 1-8 and shows that bacteriorhodopsin is synthesized as a precursor that is at least 13 amino acids longer (Met-Leu-Glu-Leu-Leu-Pro-Thr-Ala-Val-Glu-Gly-Val-Ser) at the NH2 terminus. Agarose/urea gel electrophoresis of the partially purified mRNA showed several bands; of these, a major one hybridized with 5'-[32P]cDNA. These results suggest that the bacteriorhodopsin mRNA in the partially purified preparation is homogeneous in size and that it constitutes a substantial portion of the RNA preparation subjected to electrophoresis.