Selenium in the form of selenocysteine, the rare 21st amino acid, is an important component of proteins from all kingdoms of life, the so-called selenoproteins. Selenocysteine is incorporated cotranslationally at specific UGA (stop) codons by the specific tRNAsec (SelC) First, the specific tRNAsec is loaded with serine by seryl synthetase, which is then converted to a tRNA-bound selenocysteine by selenocysteine synthase (SelA) with selenophosphate synthetase (SelD) providing the required selenol donor (1,2). Finally, the specific translation factor SelB is required, which simultaneously recognizes selenocysteine-loaded selenocysteyl-tRNAsec and a specific RNA structure close to the UGA codon that specifies the incorporation site of selenocysteine (3). This specific recognition sequence, the selenocysteine insertion sequence (SecIS), discriminates between UGA codons for selenocysteine insertion and chain termination (4). Bacterial selenoprotein synthesis has been studied mainly in Escherichia coli and a few other species, while selenoproteins appear to be present in many other taxonomic groups, often with divergent features in their selenocysteyl-tRNAs. Here, we investigate the functionality of several aberrant SelC-tRNAs from members of the Bacillaceae, Alpha- and Deltaproteobacteria, which have not been among the usual selenoprotein-forming model organisms in earlier studies. This will provide valuable data on selenocysteine metabolism and what role different structural features of SelC play in heterologous systems.
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(2) Leinfelder, W. et al. (1990) Proceedings of the National Academy of Sciences, 87(2), 543-547.
(3) Forchhammer, K. et al. (1989) Nature, 342(6248), 453-456.
(4) Heider, J. et al. (1992) The EMBO journal, 11(10), 3759-3766.