The complete amino acid sequence of elongation factor Tu of Escherichia coli has been established by sequencing overlapping cyanogen bromide and tryptic peptides. Sequence analysis of peptides was done primarily by solid-phase Edman degradation. Elongation factor Tu is a single chain polypeptide composed of 393 amino acids (Mr = 43,225). Its NH2 terminus is blocked with an acetyl group, as dete...

Decoding UGA as selenocysteine requires a unique tRNA, a specialized elongation factor, and specific secondary structures in the mRNA, termed SECIS elements. Eukaryotic SECIS elements are found in the 3' untranslated region of selenoprotein mRNAs while those in prokaryotes occur immediately downstream of UGA. Consequently, a single eukaryotic SECIS element can serve multiple UGA codons, whereas...