Selenocysteine (Sec), a rare genetically encoded amino acid with unusual 
chemical properties, is of great interest for protein engineering. Sec is 
synthesized on its cognate tRNA (tRNASec) by the concerted action of several 
enzymes. While all other aminoacyl-tRNAs are delivered to the ribosome by the 
elongation factor Tu (EF-Tu), Sec-tRNASec requires a dedicated factor, SelB. 
Incorporation of Sec into protein requires recoding of the stop codon UGA aided 
by a specific mRNA structure, the SECIS element. This unusual biogenesis 
restricts the use of Sec in recombinant proteins, limiting our ability to study 
the properties of selenoproteins. Several methods are currently available for 
the synthesis selenoproteins. Here we focus on strategies for in vivo Sec 
insertion at any position(s) within a recombinant protein in a SECIS-independent 
manner: (i) engineering of tRNASec for use by EF-Tu without the SECIS 
requirement, and (ii) design of a SECIS-independent SelB route.