In the genetic code, UGA serves as a stop signal and a selenocysteine codon, but 
no computational methods for identifying its coding function are available. 
Consequently, most selenoprotein genes are misannotated. We identified 
selenoprotein genes in sequenced mammalian genomes by methods that rely on 
identification of selenocysteine insertion RNA structures, the coding potential 
of UGA codons, and the presence of cysteine-containing homologs. The human 
selenoproteome consists of 25 selenoproteins.