Summary
Chromatin compaction differences may have a strong impact on accessibility of individual macromolecules and macromolecular assemblies to their DNA target sites. Estimates based on fluorescence microscopy with conventional resolution, however, suggested only modest compaction differences (∼2-10x) between active and inactive nuclear compartments (ANC and INC). Here, we present maps of nuclear landscapes with true-to-scale DNA-densities, ranging from <5 Mbp/µm3 to >300 Mbp/µm3. Maps were generated from individual human and mouse cell nuclei with single-molecule localization microscopy at ∼20 nm lateral and ∼100 nm axial resolution and supplemented by electron spectroscopic imaging. Microinjection of fluorescent nanobeads with sizes corresponding to macromolecular assemblies for transcription and replication into nuclei of living cells, demonstrated their localization and movements within the ANC and exclusion from the INC.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
We have exchanged the HeLa nucleus in Figure 3 for another HeLa nucleus recorded under the same conditions as the nucleus shown in figure 2 (100 nm total thickness). We moved figure 6 to supplemental materials. We have updated the affiliations of some authors and updated data in the supplemental information.
