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Molecular and Cellular Biology, July 2000, p. 4604-4613, Vol. 20, No. 13
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Eap1p, a Novel Eukaryotic Translation Initiation Factor
4E-Associated Protein in Saccharomyces cerevisiae
Gregory P.
Cosentino,1,2
Tobias
Schmelzle,3
Ashkan
Haghighat,1,
Stephen B.
Helliwell,3,
Michael N.
Hall,3 and
Nahum
Sonenberg1,*
Department of Biochemistry and McGill Cancer
Center, McGill University, Montreal, Québec H3G
1Y6,1 and Bio-Méga Research
Division, Boehringer Ingelheim (Canada) Ltd., Laval, Québec, H7S
2G5,2 Canada, and Department of
Biochemistry, Biozentrum, University of Basel, CH-4056, Basel,
Switzerland3
Received 12 July 1999/Returned for modification 2 September
1999/Accepted 27 March 2000
Ribosome binding to eukaryotic mRNA is a multistep process which is
mediated by the cap structure [m7G(5')ppp(5')N, where N is
any nucleotide] present at the 5' termini of all cellular (with the
exception of organellar) mRNAs. The heterotrimeric complex, eukaryotic
initiation factor 4F (eIF4F), interacts directly with the cap structure
via the eIF4E subunit and functions to assemble a ribosomal initiation
complex on the mRNA. In mammalian cells, eIF4E activity is regulated in
part by three related translational repressors (4E-BPs), which bind to
eIF4E directly and preclude the assembly of eIF4F. No structural counterpart to 4E-BPs exists in the budding yeast, Saccharomyces cerevisiae. However, a functional homolog (named p20) has been described which blocks cap-dependent translation by a mechanism analogous to that of 4E-BPs. We report here on the characterization of
a novel yeast eIF4E-associated protein (Eap1p) which can also regulate
translation through binding to eIF4E. Eap1p shares limited homology to
p20 in a region which contains the canonical eIF4E-binding motif.
Deletion of this domain or point mutation abolishes the interaction of
Eap1p with eIF4E. Eap1p competes with eIF4G (the large subunit of the
cap-binding complex, eIF4F) and p20 for binding to eIF4E in vivo and
inhibits cap-dependent translation in vitro. Targeted disruption of the
EAP1 gene results in a temperature-sensitive phenotype and
also confers partial resistance to growth inhibition by rapamycin.
These data indicate that Eap1p plays a role in cell growth and
implicates this protein in the TOR signaling cascade of S. cerevisiae.
*
Corresponding author. Mailing address: Department of
Biochemistry, McGill University, 3655 Drummond St., Rm. 807, Montreal, Québec H3G 1Y6, Canada. Phone: (514) 398-7274. Fax: (514)
398-1287. E-mail: nsonen{at}med.mcgill.ca.

Present address: Caprion Pharmaceuticals Inc., Montreal,
Québec, H4P 2R2,
Canada.

Present address: Department of Biology, Massachusetts Institute of
Technology, Cambridge MA 02139-4307.
Molecular and Cellular Biology, July 2000, p. 4604-4613, Vol. 20, No. 13
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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