Translational Control of Poly(A)‐Binding Protein Expression

Poly(A)‐binding protein (PABP) is important for translation of eukaryotic mRNA and may be involved in shortening of its poly(A) tract. In many eukaryotic cells, this mRNA is inefficiently translated. The 5′ untranslated region (UTR) of PABP mRNA has several adenine‐rich regions which may serve as the PABP‐binding sites to control its translation by a feed‐back mechanism. This postulate was tested by using in vitro transcribed PABP mRNA and a rabbit reticulocyte lysate cell‐free system. Results of our studies show that removal of the putative PABP‐binding sites from the 5′ UTR of this mRNA enhances its translation in the rabbit reticulocyte cell‐free system. Furthermore, in vitro translation of the full‐length PABP mRNA was inhibited by addition of purified PABP to the cell‐free system. In contrast, translation of truncated mRNA lacking the putative PABP‐binding sites at the 5′ UTR was not inhibited by exogenous PABP. We have also tested the ability of purified PABP to bind to the 5′ UTR of PABP mRNA using ultraviolet‐mediated covalent cross‐linking of RNA and proteins in vitro. Our results show that exogenous PABP binds to the 5′ UTR of its full‐length mRNA. Furthermore, incubation