Aminoacylated tmRNA from Escherichia coli interacts with prokaryotic elongation factor Tu

Abstract

Eubacterial tmRNAs (10Sa RNAs) are unique because they function, at least in Escherichia coli, both as tRNA and mRNA (for a review, see Muto et al., 1998). These ∼360 ± 40-nt-long RNAs are charged with alanine at their 3′ ends by alanyl-tRNA synthetases or AlaRS (Komine et al., 1994; Ushida et al., 1994). Alanylation occurs thanks to the presence of the equivalent of the G₃-U₇₀ pair, the major identity element for the alanylation of canonical tRNAs (Hou & Schimmel, 1988; McClain & Foss, 1988). Bacterial tmRNAs also have a short reading frame coding for 9 to 27 amino acids, depending on the species. E. coli tmRNA mediates recycling of ribosomes stalled at the end of terminatorless mRNAs, via a trans-translation process (Tu et al., 1995; Keiler et al., 1996; Himeno et al., 1997; Withey & Friedman, 1999). In E. coli, this amino acid tag is cotranslationally added to polypeptides synthesized from mRNAs lacking a termination codon, and the added 11-amino-acid C-terminal tag makes the protein a target for specific proteolysis (Keiler et al., 1996).