AUTOGENOUS TRANSLATIONAL REGULATION OF THE RIBOSOMAL MVAL1 OPERON IN THE ARCHAEBACTERIUM METHANOCOCCUS-VANNIELII

The mechanisms for regulation of ribosomal gene expression have been c haracterized in eukaryotes and eubacteria, but not yet in archaebacter ia. We have studied the regulation of the synthesis of ribosomal prote ins MvaL1, MvaL10, and MvaL12, encoded by the MvaL1 operon of Methanoc occus vannielii, a methanogenic archaebacterium. MvaL1, the homolog of the regulatory protein L1 encoded by the L11 operon of Escherichia co li, was shown to be an autoregulator of the MvaL1 operon. As in E. col i, regulation takes place at the level of translation. The target site for repression by MvaL1 was localized by site-directed mutagenesis to a region within the coding sequence of the MvaL1 gene commencing abou t 30 bases downstream of the ATG initiation codon. The MvaL1 binding s ite on the mRNA exhibits similarity in both primary sequence and secon dary structure to the L1 regulatory target site of E. coli and to the putative binding site for MvaL1 on the 23S rRNA. In contrast to other regulatory systems, the putative MvaL1 binding site is located in a se quence of the mRNA which is not in direct contact with the ribosome as part of the initiation complex. Furthermore, the untranslated leader sequence is not involved in the regulation. Therefore, we suggest that a novel mechanism of translational feedback regulation exists in M. v annielii.