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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 Factor
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.

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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