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The yeast poly(A)‐binding protein Pab1p stimulates in vitro poly(A)‐dependent and cap‐dependent translation by distinct mechanisms
Author(s) -
Otero Lucy J.,
Ashe Mark P.,
Sachs Alan B.
Publication year - 1999
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/18.11.3153
Subject(s) - national laboratory , biology , library science , physics , computer science , engineering physics
Translation initiation in extracts from Saccharomyces cerevisiae involves the concerted action of the cap‐binding protein eIF4E and the poly(A) tail‐binding protein Pab1p. These two proteins bind to translation initiation factor eIF4G and are needed for the translation of capped or polyadenylated mRNA, respectively. Together, these proteins synergistically activate the translation of a capped and polyadenylated mRNA. We have discovered that excess Pab1p also stimulates the translation of capped mRNA in extracts, a phenomenon that we define as trans ‐activation. Each of the above activities of Pab1p requires its second RNA recognition motif (RRM2). We have found that RRM2 from human PABP cannot substitute functionally for yeast RRM2. Using the differences between human and yeast RRM2 sequences as a guide, we have mutagenized yeast RRM2 and discovered residues that are required for eIF4G binding and poly(A)‐dependent translation but not for trans ‐activation. Similarly, other residues within RRM2 were found to be required for trans ‐activation but not for eIF4G binding or poly(A)‐dependent translation. These data show that Pab1p has at least two biochemically distinct activities in translation extracts.