Date of this Version
Novel mouse models were developed in which the hepatic selenoprotein population was targeted for removal by disrupting the selenocysteine (Sec) tRNA [Ser]Sec gene (trsp) and then selenoprotein expression was restored by introducing wild type or mutant trsp transgenes. The selenoprotein population was partially replaced in liver with mutant transgenes encoding mutations at either position 34 (T34->A34) or 37 (A37->G37) in tRNA [Ser]Sec. The A34 transgene product lacked the highly modified 5-methoxycarbonylmethyl-2’ O-methyluridine and its mutant base A was converted to I34. The G37 transgene product lacked the highly modified N6-isopentenyladenosine. Both mutant tRNAs lacked the 2’-methylribose at position 34 (Um34), and both supported expression of housekeeping selenoproteins (e.g., thioredoxin reductase 1) in liver, but not stress-related proteins (e.g., glutathione peroxidase 1). Thus, Um34 is responsible for synthesis of a select group of selenoproteins rather than the entire selenoprotein population. The ICA anticodon in the A34 mutant tRNA decoded Cys codons, UGU and UGC, as well as the Sec codon, UGA. However, metabolic labeling of A34 transgenic mice with 75Se revealed that selenoproteins incorporated the label from the A34 mutant tRNA, whereas other proteins did not. These results suggest that the A34 mutant tRNA did not randomly insert Sec in place of Cys, but specifically targeted selected selenoproteins. High copy numbers of A34 transgene, but not G37 transgene, were not tolerated in the absence of wild type trsp further suggesting insertion of Sec in place of Cys in selenoproteins.