Overproduction of release factor reduces spontaneous frameshifting and frameshift suppression by mutant elongation factor Tu

Abstract

Mutant forms of elongation factor Tu encoded by tufA8 and tufB103 in Salmonella typhimurium cause suppression of some but not all frameshift mutations. All of the suppressed mutations in S. typhimurium have frameshift windows ending in the termination codon UGA. Because both tufA8 and tuJB103 are moderately efficient UGA suppressors, we asked whether the efficiency of frameshifting is influenced by the level of misreading at UGA. We introduced plasmids synthesizing either one of the release factors into strains in which the tuf mutations suppress a test framesilift mutation. We found that overproduction of release factor 2 (which catalyzes release at UGA and UAA) reduced frameshifting promoted by the tuf mutations at all sites tested. However, at one of these sites, tpE91, overproduction of release factor 1 also reduced suppression. The spontaneous level of frameshift "leakiness" at three sites in trpE, each terminating in UGA, was reduced in strains carrying the release factor 2 plasmid. We conclude that both spontaneous and suppressor-enhanced reading-frame shifts are influenced by the activity of peptide chain release factors. However, the data suggest that the effect of release factor on frameshifting does not necessarily depend on the presence of the normal triplet termination signal.

A ribosomal frameshifting error during translation of the argl mRNA of Escherichla coli

“…Like programmed frameshifts that lead to required products, some frameshift errors may also happen at a high frequency and may also involve stimulatory signals, shifty sites, and slippery tRNAs. Some studies on the translational suppression of frameshift mutations have shown that frameshifting may happen at stop codons (Aulin and Hughes 1990), which must then be pause sites rather than efficient termination sites (Tate and Brown 1991), and can also be detected when ribosomes pause at certain codons made "hungry" by amino acid starvation (Kurland and Gallant 1986;Gallant 1983, 1986). The direction of a frameshift (+ 1 or -1) stimulated by amino acid starvation depends on the sequence of the mRNA surrounding the hungry codon (Lindsley and Gallant 1993).…”