Trypanosoma brucei poly(A) binding protein I cDNA cloning, expression, andbinding to 5 ' untranslated region sequence elements

Poly(A) binding protein I (PABPI) is a highly conserved eukaryotic protein that binds mRNA poly(A) tails and functions in the regulation of translatio nal efficiency and mRNA stability. As a first step in our investigation of the role(s) of mRNA poly(A) tails in posttranscriptional gene regulation in Trypanosoma brucei, we have cloned the cDNA encoding PABPI from this organ ism. The cDNA predicts a protein homologous to PABPI from other organisms a nd displaying conserved features of these proteins, including four RNA bind ing domains that span the N-terminal two-thirds of the protein. Comparison of northern blot data with the cDNA sequence indicates an unusually long 3' untranslated region (UTR) of approximately three kilobases. The 5' UTR con tains both A-rich and AU repeat regions, the former being a ubiquitous prop erty of PABPI 5' UTRs. T. brucei PABPI, expressed as a glutathione-S-transf erase fusion protein, bound to RNA comprised of its full length 5' UTR in U V cross-linking experiments. This suggests that PABPI may play an autoregul atory role in its own expression. Competition experiments indicate that the A-rich region, but not the AU repeats, are involved in this binding. (C) 1 999 Elsevier Science B.V. All rights reserved.