I am working on a project to explore histone modification discrepancies (such as lysine methylation or acetylation) between two sets of genes in the budding yeast s. cerevisiae.
The database, Yeast Nucleosome Atlas, has drawn data from several articles (Pokholok 2005 for example), which have conveyed Chip-chip studies. In the original articles data are represented by reporting relative nucleosome occupancy vs H3 or H4 (obviously a positive number).
However, the database has reported the data based on enrichment scores (H3K14ac vs H3 for exmample) and negative numbers also exist among the data. I am having difficulty interpreting these negative results, especially that for some modifications (for example H3K9ac vs H3), one group of genes (the one that allegedly should be more active) has negative mean; while the other group ( supposedly less active) has a positive mean.
Is anyone aware of the meaning of these numbers in this context? I thank you in advance
PS: Here is a link to access the database: http://cosbi3.ee.ncku.edu.tw/yna/main