TOP mRNAs are translationally inhibited by a titratable repressor in both wheat germ extract and reticulocyte lysate

Abstract

Vertebrate TOP mRNAs contain a 5P P terminal oligopyrimidine tract (5P P TOP), which is subject to selective translational repression in non-growing cells or in cell-free translation systems. In the present study, we monitored in vitro the effect of increasing amounts of a 16 nucleotides long oligoribonucleotide representing the 5P P terminus of mouse ribosomal protein S16 mRNA on the translation of TOP and non-TOP mRNAs. Our results demonstrate that the wild-type sequence (but not its mutant counterparts) derepresses the translation of mRNAs containing 5P P TOP motifs, but failed to stimulate the translation of non-TOP mRNAs, even if the latter differed only by a single nucleotide from their 5P P TOP-containing counterparts. Similar results have been obtained with both wheat germ extract and rabbit reticulocyte lysate. It appears, therefore, that translational repression of TOP mRNAs is achieved in vitro by the accumulation of a titratable repressor rather than by the loss of an activator and that this repressor recognizes multiple TOP mRNAs with a diverse set of 5P P TOP motifs.z 1999 Federation of European Biochemical Societies.

Feedback Inhibition of Poly(A)-binding Protein mRNA Translation

“…This protein may also be involved in providing the observed cell specificity toward the effect of TOP on Pabp1 mRNA translation. Although TOP binding proteins have been shown for some TOP mRNAs (55)(56)(57)(58)(59)(60)(61), their role in mRNA translation is uncertain, because the level of TOP binding activity does not change under conditions that inhibit translation of TOP mRNAs (37). It is not clear whether all TOP elements behave similarly.…”

Stress puts TIA on TOP: Figure 1.

“…Beyond regulation by signaling pathways, existence of a ''titratable'' factor regulating translation of 59TOP transcripts has been postulated, based on in vitro competition studies using synthetic RNA oligos resembling the 59TOP motif (Biberman and Meyuhas 1999). The RNA-binding proteins La (Pellizzoni et al 1997(Pellizzoni et al , 1998Cardinali et al 2003), AUF1 (Kakegawa et al 2007), and ZNF9 (Pellizzoni et al 1998;Huichalaf et al 2009), have been proposed as candidates that selectively regulate translation of 59TOP transcripts.…”

TOPs and their regulation

“…Indeed, the selective repression of a TOP mRNA in translation extracts can be relieved by a synthetic TOP RNA oligonucleotide, arguing for the existence of a titratable repressor protein [25]. Although proteins have been shown to interact with 5 -TOP sequences, the functional significance of these interactions remains unclear [2].…”