We report in vivo analysis of histone and RNA polymerase II (pol II) occupancy at the 601 element, which functions as a strong in vitro nucleosome-positioning element and transcriptional pause site. Surprisingly, nucleosomes were not strongly positioned over the 601 element inserted either within a yeast chromosomal open reading frame (ORF) (GAL1-YLR454W) or in an intergenic region. In fact 601 within GAL1-YLR454W was actually depleted of histones relative to flanking sequences and did not cause pol II pausing. Upstream of an inserted 601 element within GAL1-YLR454W, a positioned nucleosome was formed whose location depended on transcriptional history; it shifted after a round of activation and repression. Transcriptional activation caused histone eviction throughout the GAL1-YLR454W ORF, except at 601, where there was no loss and some net histone deposition. In contrast, a second round of activation after glucose shutoff caused histone eviction both at 601 and elsewhere in the ORF. We conclude that the intrinsic high-affinity histone-DNA interactions at 601 do not necessarily play a dominant role in establishing nucleosomes or pol II pause sites within a coding region in vivo and that transcriptional history can have an important influence on histone occupancy flanking this sequence.

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Journal Article | Research Support, N.I.H., Extramural

Authors

Perales R, Zhang L, Bentley D

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