Fig. 1.

Testing positional memory. (A) Binding of TetR to its site (TetO) within the GAL10 gene tethers an attenuated version of E. coli biotin ligase (split BirA) to the site. AviTagged histone H3 (flags) in ∼4 adjacent nucleosomes becomes biotinylated (green flags). (B) After 2 rounds of cell division, the shape of the biotinylation profile does not change, although the signal becomes diluted. Mutations in the MCM2 and DPB3 histone chaperones required for equal reassembly of nucleosomes between leading and lagging strand do not change the shape of the profile, although they further weaken the signal. High-level transcription through GAL10 induced by growth in galactose weakens the signal but has no effect on its shape. Thus, nucleosomes remember their position through replication and transcription.