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.