Figure 1. Chromatin proteins to scale.
Protein complexes sketched from 3D structures are drawn, and the segment of DNA that each protects is indicated. From left to right: nucleosome (wrapping 150 bp), nucleosome with chromatin remodeler (1) (120 bp footprint), transcription factor (~20 bp footprint), RNAPII and Mediator (2) (80 bp footprint), and a replisome (3) (60 bp footprint). A nucleosome depleted region (NDR) is usually found at promoters of active genes. The wrapping of DNA around a nucleosome causes the DNA to be negatively supercoiled, indicated by black “-” sign below the nucleosomes. The movement of remodelers, RNAPII, and replisome propagates positive supercoiling in front of these complexes and negative supercoiling behind them, indicated by red, green, and gray “+” and “-” signs for supercoiling and arrows for direction of movement of these complexes (4). Lengths of DNA are not drawn to scale as some structures like nucleosome wrap DNA.
