Nucleotide sequence of a gene cluster encoding NusG and the L11-L1-L10-L12 ribosomal proteins from the thermophilic archaeon Sulfolobus solfataricus

Control of ribosomal protein L1 synthesis in mesophilic and thermophilic archaea

The mechanisms for the control of ribosomal protein synthesis have been characterized in detail in Eukarya and in Bacteria. In Archaea, only the regulation of the MvaL1 operon (encoding ribosomal proteins MvaL1, MvaL10, and MvaL12) of the mesophilic Methanococcus vannielii has been extensively investigated. As in Bacteria, regulation takes place at the level of translation. The regulator protein MvaL1 binds preferentially to its binding site on the 23S rRNA, and, when in excess, binds to the regulatory target site on its mRNA and thus inhibits translation of all three cistrons of the operon. The regulatory binding site on the mRNA, a structural mimic of the respective binding site on the 23S rRNA, is located within the structural gene about 30 nucleotides downstream of the ATG start codon. MvaL1 blocks a step before or at the formation of the first peptide bond of MvaL1. Here we demonstrate that a similar regulatory mechanism exists in the thermophilic M. thermolithotrophicus and M. jannaschii. The L1 gene is cotranscribed together with the L10 and L11 gene, in all genera of the Euryarchaeota branch of the Archaea studied so far. A potential regulatory L1 binding site located within the structural gene, as in Methanococcus, was found in Methanobacterium thermoautotrophicum and in Pyrococcus horikoshii. In contrast, in Archaeoglobus fulgidus a typical L1 binding site is located in the untranslated leader of the L1 gene as described for the halophilic Archaea. In Sulfolobus, a member of the Crenarchaeota, the L1 gene is part of a long transcript (encoding SecE, NusG, L11, L1, L10, L12). A previously suggested regulatory L1 target site located within the L11 structural gene could not be confirmed as an L1 binding site.

MvaL1 autoregulates the synthesis of the three ribosomal proteins encoded on the MvaL1 operon of the archaeon Methanococcus vannielii by inhibiting its own translation before or at the formation of the first peptide bond

The control of ribosomal protein synthesis has been investigated extensively in Eukarya and Bacteria. In Archaea, only the regulation of the MvaL1 operon (encoding ribosomal proteins MvaL1, MvaL10 and MvaL12) of Methanococcus vannielii has been studied in some detail. As in Escherichia coil, regulation takes place at the level of translation. MvaL1, the homologue of the regulatory protein L1 encoded by the L11 operon of E. coli, was shown to be an autoregulator of the MvaL1 operon. The regulatory MvaL1 binding site on the mRNA is located about 30 nucleotides downstream of the ATG start codon, a sequence that is not in direct contact with the initiating ribosome. Here, we demonstrate that autoregulation of MvaL1 occurs at or before the formation of the first peptide bond of MvaL1. Specific interaction of purified MvaL1 with both 23S RNA and its own mRNA is confirmed by filter binding studies. In vivo expression experiments reveal that translation of the distal MvaL10 and MvaL12 cistrons is coupled to that of the MvaL1 cistron. A mRNA secondary structure resembling a canonical L10 binding site and preliminary in vitro regulation experiments had suggested a co-regulatory function of MvaL10, the homologue of the regulatory protein L10 of the beta-operon of E. coil. However, we show that MvaL10 does not have a regulatory function.