Affiliations: Lehrstuhl für Mikrobiologie der Universität
München, Institut für Genetik und Mikrobiologie, Maria Ward Stra§e 1a,
D-80638 Munich, Germany
Abstract: The availability of the genome sequences from several archaea has
facilitated the identification of the encoded selenoproteins and also of most
of the components of the machinery for selenocysteine biosynthesis and
insertion. Until now, selenoproteins have been identified solely in species of
the genera {\it Methanococcus (M.)} and {\it Methanopyrus}. Apart from
selenophosphate synthetase, they include only enzymes with a function in energy
metabolism. Like in bacteria and eukarya, selenocysteine insertion is directed
by a UGA codon in the mRNA and involves the action of a specific tRNA and of
selenophosphate as the selenium donor. Major differences to the bacterial
system, however, are that no homolog for the bacterial selenocysteine synthase
was found and, especially, that the SECIS element of the mRNA is positioned in
the 3' nontranslated region. The characterisation of a homolog for the
bacterial SelB protein showed that it does not bind to the SECIS element
necessitating the activity of at least a second protein. The use of the genetic
system of {\it M. maripaludis} allowed the heterologous expression of a
selenoprotein gene from {\it M. jannaschii} and will facilitate the elucidation
of the mechanism of the selenocysteine insertion process in the future.
