Knowing when not to stop: selenocysteine incorporation in eukaryotes

The regulation of translation frequently involves protein-RNA interactions. An intriguing example of this is the alternative decoding of UGA, typically a stop codon, as selenocysteine. Two RNA structures, the mRNA selenocysteine insertion sequence (SECIS element) and a unique selenocysteyl-tRNA, are required for this process. In prokaryotes, a single RNA-binding protein, a selenocysteine-specific elongation factor, interacts with both the tRNA and mRNA to confer decoding. Whether eukaryotes use a similar mechanism is currently the subject of intense investigation.