Densitometric scan of MNase sensitive regions of the MFA2 promoter.

(A and B) Relative MNase sensitivity is expressed graphically from scans of the gels shown in Figure S1. Trace A: transcribed strand (TS); Trace B: non-transcribed strand (NTS). The positioned nucleosomes observed in wild type cells are represented by ellipses N-1 and N-2. (C) Schematic representation of the assay in D. The middle of nucleosome N-2 of MFA2 promoter has a single RsaI restriction site within the HaeIII restriction fragment. The probe shown detects either the full-length 599 bp of HaeIII fragment or 419 bp of RsaI and HaeIII double digested fragment. The protection rendered by nucleosome N-2 limits the accessibility of RsaI to the site. (D) Southern blot analysis of RsaI accessibility to the MFA2 promoter N-2 site. Lane −: naked DNA digested by HaeIII only; lane +: naked DNA digested by both HaeIII and RsaI. Lanes 1–8 represent HaeIII degisted DNA purified from RsaI digested chromatin samples from the strains listed. The lower panel shows the data graphically.