text: Studies in 2007 have catalogued nucleosome positions in yeast and shown that nucleosomes are depleted in promoter regions and origins of replication.
  About 80% of the yeast genome appears to be covered by nucleosomes and the pattern of nucleosome positioning clearly relates to DNA regions that regulate transcription, regions that are transcribed and regions that initiate DNA replication. Most recently, a new study examined dynamic changes in nucleosome repositioning during a global transcriptional reprogramming event to elucidate the effects on nucleosome displacement during genome-wide transcriptional changes in yeast (Saccharomyces cerevisiae). The results suggested that nucleosomes that were localized to promoter regions are displaced in response to stress (like heat shock). In addition, the removal of nucleosomes usually corresponded to transcriptional activation and the replacement of nucleosomes usually corresponded to transcriptional repression, presumably because transcription factor binding sites became more or less accessible, respectively. In general, only one or two nucleosomes were repositioned at the promoter to effect these transcriptional changes. However, even in chromosomal regions that were not associated with transcriptional changes, nucleosome repositioning was observed, suggesting that the covering and uncovering of transcriptional DNA does not necessarily produce a transcriptional event. After transcription, the rDNA region has to protected from any damage, it suggested HMGB proteins play a major role in protecting the nucleosome free region.