Figure 1.

Comparison of chromatin structures by indirect-end-label analysis at three telomeres of Saccharoyces cerevisiae. (A) Schematic of a URA3-yEGFP marked native telomere showing relevant restriction sites. Probes used for indirect end-labelling are indicated by arrows. (B) The subtelomeric chromatin structure of the truncated VIIL and native IIIR and XIL telomeres of S. cerevisiae was analysed by MNase digestion and indirect end labelling with the indicated probe. The chromatin structure of an isogenic strain containing the URA3-yEGFP construct at the native URA3 locus was also analysed. A control MNase digest of deproteinized DNA (D), and marker bands generated by digestion with StuI and PstI (M) are also shown. The position of the inserted URA3-yEGFP cassette is shown by a light grey box with hatching to indicate the URA3-yEGFP CDS; the TATA box (T) is indicated with a black bar. Restriction sites are numbered from the URA3 start codon. Three promoter-associated hypersensitive sites are indicated by black arrow heads and an array of evenly spaced hypersensitive sites, present at the VIIL and XIL telomeres, by white arrow heads. Inferred nucleosome positions are shown by ovals. The most telomere-proximal open reading frames, YGL256W (e), YKL224C (f), and YCR107W (g) are indicated by arrows to the left of each blot. (C) The chromatin structure downstream of the URA3-yEGFP reporter was detected using a probe on the telomere proximal side of the StuI site. Marker bands were obtained by digestion with StuI and XmaI. MNase hypersensitive sites adjacent to the core X binding sites are indicated by grey arrows. A schematic of the IIIR and XIL telomeres is shown with the core X ACS and Abf1 binding sites indicated by black bars. The truncation end VIIL is identical except that it lacks the core X and STR repeats.