Revealing the Mechanism of HSP104 Transcription Initiation in the ...

Regulation of Hsf1
As explained in “Introduction”, mechanisms underlying Hsf1
activation/regulation are not revealed. Many regulators of Hsf1 have been identified,
that impose phosphorylation, sumoylation, and oxidation, but none of these
modifications seems critical. Furthermore, elements of the basal transcription
machinery that are required for Hsf1 activity were hitherto not identified. As
described in the previous section, we monitored the activity of the HSE-LacZ reporter
gene in various mutants. This reporter reflects the activity of Hsf1 only, because it
contains only HSEs upstream to the minimal promoter. Therefore, in a strain
demonstrating poor activity of this reporter, Hsf1 activity is compromised (Table 6, of
which 20 mutant strains exclusively affect activity of the HSE-LacZ reporter). Thirty
nine such strains were identified. We did not find even one strain with spontaneous
increased HSE-LacZ activity. Since strains identified are mutated in components of
the basal transcription machinery, they may be compromised in activation of many
stress-induced activators and not specifically Hsf1. In order to assess whether the
effects observed are specific to Hsf1, we tested in some of the strains the activity of
the SV40-LacZ reporter which is activated solely by the yAP-1 transcriptional
activator (Table 7). Except for one strain (sas3∆), all other 11 strains with reduced
HSE-LacZ activity that were tested, showed activity levels of the SV40-LacZ gene
similar to that of wild type (Table 7).
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