Schizosaccharomyces pombe genome-wide nucleosome mapping reveals positioning mechanisms distinct from those of Saccharomyces cerevisiae

Positioned nucleosomes limit the access of proteins to DNA and implement regulatory features encoded in eukaryotic genomes. Here we have generated the first genome-wide nucleosome positioning map for Schizosaccharomyces pombe and annotated transcription start and termination sites genome wide. Using this resource, we found surprising differences from the previously published nucleosome organization of the distantly related yeast Saccharomyces cerevisiae. DNA sequence guides nucleosome positioning differently: for example, poly(dA-dT) elements are not enriched in S. pombe nucleosome-depleted regions. Regular nucleosomal arrays emanate more asymmetrically-mainly codirectionally with transcription-from promoter nucleosome-depleted regions, but promoters harboring the histone variant H2A.Z also show regular arrays upstream of these regions. Regular nucleosome phasing in S. pombe has a very short repeat length of 154 base pairs and requires a remodeler, Mit1, that is conserved in humans but is not found in S. cerevisiae. Nucleosome positioning mechanisms are evidently not universal but evolutionarily plastic.