Control of ribosomal protein L1 synthesis in mesophilic and thermophilic archaea

The mechanisms for the control of ribosomal protein synthesis have been cha racterized in detail in Eukarya and in Bacteria. In Archaea, only the regul ation of the MvaL1 operon (encoding ribosomal proteins MvaL1, MvaL10, and M vaL12) of the mesophilic Methanococcus vannielii has been extensively inves tigated. As in Bacteria, regulation takes place at the level of translation . The regulator protein MvaL1 binds preferentially to its binding site on t he 23S rRNA, and, when in excess, binds to the regulatory target site on it s mRNA and thus inhibits translation of all three cistrons of the operon. T he regulatory binding site on the mRNA, a structural mimic of the respectiv e 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 befo re or at the formation of the first peptide bond of MvaL1. Here we demonstr ate that a similar regulatory mechanism exists in the thermophilic M. therm olithotrophicus and M. jannaschii. The L1 gene is cotranscribed together wi th the L10 and L11 gene, in all genera of the Euryarchaeota branch of the A rchaea studied so far. A potential regulatory L1 binding site located withi n the structural gene, as in Methanococcus, was found in Methanobacterium t hermoautotrophicum and in Pyrococcus horikoshii. In contrast, in Archaeoglo bus fulgidus a typical L1 binding site is located in the untranslated leade r of the LI gene as described for the halophilic Archaea. In Sulfolobus, a member of the Crenarchaeota, the LI gene is part of a long transcript (enco ding SecE, NusG, L11, L1, L10, L12). A previously suggested regulatory L1 t arget site located within the L11 structural gene could not be confirmed as an L1 binding site.