Novel selenoproteins identified in silico and in vivo by using a conservedRNA structural motif

Selenocysteine is incorporated into selenoproteins by an in-frame UGA codon whose readthrough requires the selenocysteine insertion sequence (SECIS), a conserved hairpin in the 3'-untranslated region of eukaryotic selenoprote in mRNAs, To identify new selenoproteins, we developed a strategy that obvi ates the need for prior amino acid sequence information, A computational sc reen was used to scan nucleotide sequence data bases for sequences presenti ng a potential SECIS secondary structure, The computer-selected hairpins we re then assayed in vivo for their functional capacities, and the cDNAs corr esponding to the SECIS winners were identified. Four of them encoded novel selenoproteins as confirmed by in vivo experiments. Among these, SelZf1 and SelZf2 share a common domain with mitochondrial thioredoxin reductase-g. T he three proteins, however, possess distinct N-terminal domains, We found t hat another protein, SelX, displays sequence similarity to a protein involv ed in bacterial pilus formation. For the first time, four novel selenoprote ins were discovered based on a computational screen for the RNA hairpin dir ecting selenocysteine incorporation.