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Molecular and Cellular Biology, February 1999, p. 1416-1426, Vol. 19, No. 2
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

The Saccharomyces cerevisiae Homologue of Mammalian Translation Initiation Factor 6 Does Not Function as a Translation Initiation Factordagger

Kausik Si and Umadas Maitra*

Department of Developmental and Molecular Biology, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461

Received 11 August 1998/Returned for modification 12 October 1998/Accepted 27 October 1998

Eukaryotic translation initiation factor 6 (eIF6) binds to the 60S ribosomal subunit and prevents its association with the 40S ribosomal subunit. The Saccharomyces cerevisiae gene that encodes the 245-amino-acid eIF6 (calculated Mr 25,550), designated TIF6, has been cloned and expressed in Escherichia coli. The purified recombinant protein prevents association between 40S and 60S ribosomal subunits to form 80S ribosomes. TIF6 is a single-copy gene that maps on chromosome XVI and is essential for cell growth. eIF6 expressed in yeast cells associates with free 60S ribosomal subunits but not with 80S monosomes or polysomal ribosomes, indicating that it is not a ribosomal protein. Depletion of eIF6 from yeast cells resulted in a decrease in the rate of protein synthesis, accumulation of half-mer polyribosomes, reduced levels of 60S ribosomal subunits resulting in the stoichiometric imbalance in the 40S/60S subunit ratio, and ultimately cessation of cell growth. Furthermore, lysates of yeast cells depleted of eIF6 remained active in translation of mRNAs in vitro. These results indicate that eIF6 does not act as a true translation initiation factor. Rather, the protein may be involved in the biogenesis and/or stability of 60S ribosomal subunits.

* Corresponding author. Mailing address: Department of Developmental and Molecular Biology, Albert Einstein College of Medicine of Yeshiva University, Jack and Pearl Resnick Campus, 1300 Morris Park Ave., Bronx, NY 10461. Phone: (718) 430-3505. Fax: (718) 430-8567. E-mail: maitra{at}aecom.yu.edu.

dagger This paper is dedicated to Jerard Hurwitz on the occasion of his 70th birthday for his enormous original scientific contributions in the field of nucleic acid biosynthesis.

Molecular and Cellular Biology, February 1999, p. 1416-1426, Vol. 19, No. 2
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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