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Journal of Bacteriology, May 1999, p. 3136-3143, Vol. 181, No. 10
Department of Biomolecular
Chemistry2 and Department of
Bacteriology,1 University of Wisconsin, Madison,
Wisconsin 53706
Received 4 February 1999/Accepted 16 March 1999
Genes encoding ribosomal proteins and other components of the
translational apparatus are coregulated to efficiently adjust the
protein synthetic capacity of the cell. Ssb, a Saccharomyces cerevisiae Hsp70 cytosolic molecular chaperone, is associated with the ribosome-nascent chain complex. To determine whether this
chaperone is coregulated with ribosomal proteins, we studied the mRNA
regulation of SSB under several environmental conditions. Ssb and the ribosomal protein rpL5 mRNAs were up-regulated upon carbon
upshift and down-regulated upon amino acid limitation, unlike the mRNA
of another cytosolic Hsp70, Ssa. Ribosomal protein and Ssb mRNAs, like
many mRNAs, are down-regulated upon a rapid temperature upshift. The
mRNA reduction of several ribosomal protein genes and Ssb was delayed
by the presence of an allele, EXA3-1, of the gene encoding
the heat shock factor (HSF). However, upon a heat shock the
EXA3-1 mutation did not significantly alter the reduction
in the mRNA levels of two genes encoding proteins unrelated to the
translational apparatus. Analysis of gene fusions indicated that the
transcribed region, but not the promoter of SSB, is
sufficient for this HSF-dependent regulation. Our studies suggest that
Ssb is regulated like a core component of the ribosome and that HSF is
required for proper regulation of SSB and ribosomal mRNA
after a temperature upshift.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
SSB, Encoding a Ribosome-Associated Chaperone, Is
Coordinately Regulated with Ribosomal Protein Genes
*
Corresponding author. Mailing address: Department of
Biomolecular Chemistry, 587 Medical Science Center, 1300 University
Ave., Madison, WI 53706. Phone: (608) 263-7105. Fax: (608) 262-5253. E-mail: ecraig{at}facstaff.wisc.edu.
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