Nucleosome loss activates yeast downstream promoters in vivo

M Han, M Grunstein - Cell, 1988 - cell.com
M Han, M Grunstein
Cell, 1988cell.com
Nucleosome depletion can be made to occur in yeast by addition of glucose to strains
containing the histone H4 gene under GAL promoter control. This leads to the activation of
downstream promoter elements (TATA box and initiation, I, region) of three different
regulated yeast promoters fused to the E. coli IacZ gene. Nucleosome loss activates the
PH05 downstream element in the presence or absence of the upstream activator sequences
(UAS) through which PH05 induction is normally mediated. The cytochrome C (CYC7) and …
Nucleosome depletion can be made to occur in yeast by addition of glucose to strains containing the histone H4 gene under GAL promoter control. This leads to the activation of downstream promoter elements (TATA box and initiation, I, region) of three different regulated yeast promoters fused to the E. coli IacZ gene. Nucleosome loss activates the PH05 downstream element in the presence or absence of the upstream activator sequences (UAS) through which PH05 induction is normally mediated. The cytochrome C (CYC7) and galactokinase (GAL7) promoters are normally repressed by glucose through their UAS elements. However, when these UAS are deleted, the remaining downstream promoters are also activated by glucose-mediated nucleosome loss. These data suggest that nucleosome loss increases transcription initiation and subsequent elongation in vivo. They also indicate that the proteins which recognize the downstream promoter are activated and functional, at least in part, even in the absence of the UAS complex.
Nucleosomes are the building units of a chromosome and consist of an octamer containing two molecules each of core histones H2A, H2l3, H3, and H4. Around this octamer are coiled approximately two turns or some 146 bp of DNA (Richmond et al., 1984). Whether nucleosomes modulate transcription in living cells is an unanswered question. The experiments of Schlissel and Brown (1984) have shown that formation of a nucleosome structure on 5s genes in vitro, prior to assembly of a stable active transcription complex, represses RNA synthesis by RNA polymerase III. However, if the transcription complex is formed prior to nucleosome assembly, 5S RNA synthesis can take place. Similar results were obtained with nucleosomes and a transcription complex that includes RNA polymerase II (Workman and Roeder, 1987). Furthermore, RNA polymerase II promoter sequences, packaged into nucleosomes, were resistant to transcription by added SP6 or mammalian RNA polymerase(Larch et al., 1987). These data suggest that nucleosomes can repress initiation of transcription in vitro. However, it is unknown whether nucleosomes repress transcription in vivo. To address this problem, we constructed yeast strains that allow the repression of histone synthesis and result in the subsequent loss of nucleosomes in vivo. For example, when the histone H4 (or H2B) gene in these strains
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