Figure 1.

Unique chromatin structure at telomeres. (A) Schematic of fission yeast telomere components. S. pombe shelterin, comprising Taz1, Rap1, Poz1, Tpz1, Ccq1 and Pot1, is highly similar to mammalian shelterin. (B) Schematic of subtelomeric (STE1 and STE2) and telomeric (Telo) regions, with distance from chromosome end indicated above. Probes used are depicted as lines below each region (not to scale). Below the schematic is a ball-and-stick diagram of the dimensions of the telosome mapped in this study. Circles indicate canonical nucleosomes; ovals depict the telosome. (C) Gel and Southern blot analysis of subtelomeric and telomeric regions following treatment of intact chromatin with increasing concentrations of MNase (‘chromatin’). Naked DNA was also treated with MNase to control for sequence specificity. Duplicate samples were electrophoresed on the same gel and EtBr stained. The EtBr images in the left and 4th panel show the pattern of bulk genomic chromatin, attesting to the intactness of the chromatin preparation. Each gel was subjected to Southern blot analysis using the probes indicated below each panel. The STE2 probe was applied after stripping the Telo blot. The ball-and-stick schematics to the right of each blot depict the chromatin structure, to scale with the blots; circles and ovals as in (B) with probe positions indicated by lines whose colors correspond to the designations in (B). Note that the ball-and-stick diagrams reflect the different probe positions for each blot; for instance, the STE1 probe hybridizes to more centromere-proximal genomic regions that start to contain canonical nucleosomes, hence the appearance of mononucleosome bands on the STE1-probed blot.