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Molecular and Cellular Biology, February 2001, p. 916-927, Vol. 21, No. 3
Department of Microbiology and
Immunology1 and Department of
Biochemistry and Howard Hughes Medical
Institute,2 Stanford University School of
Medicine, Stanford, California 94305
Received 23 May 2000/Returned for modification 25 October
2000/Accepted 31 October 2000
The global gene expression program that accompanies the adaptation
of Saccharomyces cerevisiae to an abrupt transfer from a
fermentable to a nonfermentable carbon source was characterized by
using a cDNA microarray to monitor the relative abundances and
polysomal distributions of mRNAs. Features of the program included a
transient reduction in global translational activity and a severe
decrease in polysome size of transcripts encoding ribosomal proteins.
While the overall translation initiation of newly synthesized and
preexisting mRNAs was generally repressed after the carbon source
shift, the mRNA encoded by YPL250C was an exception in that
it selectively mobilized into polysomes, although its relative
abundance remained unchanged. In addition, splicing of HAC1
transcripts, which has previously been reported to occur during
accumulation of unfolded proteins in the endoplasmic reticulum, was
observed after the carbon shift. This finding suggests that the
nonconventional splicing complex, composed of the kinase-endonuclease Ire1p and the tRNA ligase Rlg1p, was activated. While spliced HAC1 transcripts mobilized into polysomes, the vast
majority of unspliced HAC1 RNA accumulated in nonpolysomal
fractions before and after the carbon source shift, indicating that
translation of unspliced HAC1 RNA is blocked at the
translation initiation step, in addition to the previously reported
elongation step. These findings reveal that S. cerevisiae
reacts to the carbon source shift with a remarkable variety of
responses, including translational regulation of specific mRNAs and
activation of specific enzymes involved in a nonconventional splicing mechanism.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.3.916-927.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Global and Specific Translational Regulation in the
Genomic Response of Saccharomyces cerevisiae to a Rapid
Transfer from a Fermentable to a Nonfermentable Carbon Source

*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305. Phone: (650) 498-7076. Fax: (650) 498-7147. E-mail
for Peter Sarnow: psarnow{at}leland.stanford.edu. E-mail for Patrick O. Brown: pbrown{at}cmgm.stanford.edu.
Present address: Department of Biochemistry and Biophysics,
University of California at San Francisco, San Francisco, California 94116.
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