Prokaryotic-style frameshifting in a plant translation system: conservation of an unusual single-tRNA slippage event.

Ribosomal frameshifting signals are found in mobile genetic elements, viruses and cellular genes of prokaryotes and eukaryotes. Typically they comprise a slippery sequence, X XXY YYZ, where the frameshift occurs, and a stimulatory mRNA element. Here we studied the influence of host translational environment and the identity of slippery sequence-decoding tRNAs on the frameshift mechanism. By expressing candidate signals in Escherichia coli, and in wheatgerm extracts depleted of endogenous tRNAs and supplemented with prokaryotic or eukaryotic tRNA populations, we show that when decoding AAG in the ribosomal A-site, E.coli tRNA(Lys) promotes a highly unusual single-tRNA slippage event in both prokaryotic and eukaryotic ribosomes. This event does not appear to require slippage of the adjacent P-site tRNA, although its identity is influential. Conversely, asparaginyl-tRNA promoted a dual slippage event in either system. Thus, the tRNAs themselves are the main determinants in the selection of single- or dual-tRNA slippage mechanisms. We also show for the first time that prokaryotic tRNA(Asn) is not inherently 'unslippery' and induces efficient frameshifting when in the context of a eukaryotic translation system.