Heterologous expression of archaeal selenoprotein genes directed by the SECIS element located in the 3 ' non-translated region

Previous in silico analysis of selenoprotein genes in Archaea revealed that the selenocysteine insertion (SECIS) motif necessary to recode UGA with se lenocysteine was not adjacent to the UGA codon as is found in Bacteria, Rat her, paralogous stem-loop structures are located in the 3' untranslated reg ion (3' UTR), reminiscent of the situation in Eukarya, To assess the functi on of such putative SECIS elements, the Methanococcus jannaschii MJ0029 (fr uA, which encodes the A subunit of the coenzyme F-420-reducing hydrogenase) mRNA was mapped in vivo and probed enzymatically in vitro. It was shown th at the SECIS element is indeed transcribed as part of the respective mRNA a nd that its secondary structure corresponds to that predicted by RNA foldin g programs. Its ability to direct selenocysteine insertion in vivo was demo nstrated by the heterologous expression of MJ0029 in Methanococcus maripalu dis, resulting in the synthesis of an additional selenoprotein, as analysed by Se-75 labelling. The selective advantage of moving the SECIS element in the untranslated region may confer the ability to insert more than one sel enocysteine into a single polypeptide, Evidence for this assumption was pro vided by the finding that the M. maripaludis genome contains an open readin g frame with two in frame TGA codons, followed by a stem-loop structure in the 3' UTR of the mRNA that corresponds to the archaeal SECIS element.