EXPERIMENTAL FIGURE 8-23 The extended and condensed forms of extracted chromatin have very different appearances in electron micrographs. (a) Chromatin isolated in low-ionic-strength buffer has an extended “beads-on-a-string” appearance. The “beads” are nucleosomes (10 nm in diameter) and the “string” is connecting (linker) DNA. (b) Chromatin isolated in buffer with a physiological ionic strength (0.15 M KCl) appears as a condensed fiber 30 nm in diameter.

[Part (a) courtesy of Steven McKnight and Oscar Miller, Jr. Part (b) courtesy of Barbara Hamkalo and J. B. Rattner.]