Halobacterial S9 operon. Three ribosomal protein genes are cotranscribed with genes encoding a tRNA(Leu), the enolase, and a putative membrane protein in the archaebacterium Haloarcula (Halobacterium) marismortui.

In the eubacterium Escherichia coli the genes for the ribosomal proteins L13 and S9 form an operon consisting of two genes. The corresponding operon of the archaebacterium Haloarcula marismortui (Halobacterium marismortui was recently reassigned to the genus Haloarcula [Oren, A., Ginzburg, M., Ginzburg, B. Z., Hochstein, L. I., and Volcani, B. E. (1990) Int. J. Syst. Bacteriol. 40, 209-210] and is now called Haloarcula marismortui) which is presented here, is much larger encoding three ribosomal proteins (HL29, HmaL13, HmaS9), a tRNA(Leu), the glycolytic enzyme enolase (HmaEno), a putative membrane protein (OrfMSG), and two not yet identified open reading frames (OrfMMV, OrfMNA). The nucleotide sequence of 3931 base pairs has been established. Northern analysis revealed the existence of a polycistronic mRNA (3.7 kilobases) demonstrating that the transcription of a gene of the glycolytic pathway is coupled to the transcription of ribosomal protein genes. Upstream of the first gene of the operon (tRNA(Leu)) a promoter structure typical for the extreme halophilic archaebacteria was detected and downstream of the last gene (OrfMSG) a terminator structure was present. As shown by S1-nuclease mapping, a tRNA-mRNA transcript as well as the mRNA alone was present in vivo. The transcriptional start point and the tRNA-mRNA cleavage point are shown to be almost identical to the 5' and 3' ends, respectively, of the putative mature tRNA. The C-terminal part of the OrfMSG protein shows a significant similarity to the vertebrate laminin receptor protein.