Visualizing chromatin organization and dynamics during transcription. (A) The arrays are composed of a single human or mouse BAC with lac operator sites incorporated for visualization. (Red dots indicate continuation of the repeat for 10 copies). (B) Decondensation occurs upon transcriptional induction of one or more of the genes in the BAC, yielding a linear trajectory of spots. Even after decondensation, compaction levels are still far above those of a 30-nm fiber. (C) Three different types of association with speckles were observed. (D) Independent, random motion of individual GFP spots was detected (for visibility, the arrows depicting this motion are larger than the actual movements).