Volume 271,
Number 5,
Issue of February 2, 1996 pp. 2717-2723
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.
Multimerization
of Hsp42p, a Novel Heat Shock Protein of Saccharomyces
cerevisiae, Is Dependent on a Conserved Carboxyl-terminal
Sequence
(Received for publication, August 10,
1995; and in revised form, November 7, 1995)
David
Wotton ,
Katie
Freeman ,
David
Shore
Rap1p is a transcriptional regulator of Saccharomyces
cerevisiae, which plays roles in both transcriptional activation
and silencing. To identify proteins involved in Rap1p-dependent
regulation of transcription, we used the two-hybrid system to screen
for Rap1p-interacting proteins. Two of the clones isolated from this
screen encode a truncated protein with homology to small heat shock
proteins (HSPs). Here we present an analysis of this novel S.
cerevisiae HSP, which we name Hsp42p. Expression of HSP42 is regulated by a range of stress conditions similar to S.
cerevisiae HSP26, with which Hsp42p shares most homology. However, HSP42 expression is more sensitive to increased salt
concentration and to starvation and, in contrast to HSP26 is
expressed in unstressed cells. Hsp42p interacts with itself in the
two-hybrid assay. This interaction is dependent on a hydrophobic region
which is conserved among small HSPs. Using bacterially expressed Hsp42p
fusion proteins, we demonstrate that this is a direct interaction.
Fractionation of yeast protein extracts by size demonstrates that all
of the Hsp42p in these extracts is present in complexes with a
molecular mass of greater than 200 kDa, suggesting that Hsp42p exists
in high molecular mass complexes.
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