Internal initiation drives the synthesis of Ure2 protein lacking the prion domain and affects [URE3] propagation in yeast cells |
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Authors: | Komar Anton A Lesnik Thierry Cullin Christophe Merrick William C Trachsel Hans Altmann Michael |
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Institution: | Institut für Biochemie und Molekularbiologie, Universit?t Bern, Buehlstrasse 28, 3012 Bern, Switzerland. aak11@po.cwru.edu |
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Abstract: | The URE3] phenotype in Saccharomyces cerevisiae is caused by the inactive, altered (prion) form of the Ure2 protein (Ure2p), a regulator of nitrogen catabolism. Ure2p has two functional domains: an N-terminal domain necessary and sufficient for prion propagation and a C-terminal domain responsible for nitrogen regulation. We show here that the mRNA encoding Ure2p possesses an IRES (internal ribosome entry site). Internal initiation leads to the synthesis of an N-terminally truncated active form of the protein (amino acids 94-354) lacking the prion-forming domain. Expression of the truncated Ure2p form (94-354) mediated by the IRES element cures yeast cells of the URE3] phenotype. We assume that the balance between the full-length and truncated (94-354) Ure2p forms plays an important role in yeast cell physiology and differentiation. |
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