A Reply to "MNase-Sensitive Complexes in Yeast: Nucleosomes and Non-histone Barriers," by Chereji et al.

In this issue of Molecular Cell, Chereji et al. (2017) present new data on MNase-sensitive particles previously identified upstream of transcription start sites at many promoters in budding yeast, and they argue, based upon negative histone-ChIP results, that they are non-nucleosomal signals generated by transcription factors (TFs). We show instead, based upon functional experiments where the relevant TFs are rapidly depleted, that this explanation does not hold, and we argue instead that histone ChIP and chemical cleavage assays have a limited capacity to capture these highly dynamic, MNase-sensitive "fragile" nucleosomes.