HU is the most conserved nucleoid-associated protein in eubacteria and has been implicated as a key player in global chromosome organization. The mechanism of HU-mediated nucleoid organization, however, remains poorly understood. Using single molecule tracking coupled with genetic manipulations, we characterized the dynamics of HU in live Escherichia coli cells. We found that native HU dimers bind and unbind chromosomal DNAs weakly and transitorily across the entire nucleoid volume but remain nucleoid-localized, reminiscent of random diffusion in a liquid phase-separated, membrane-less "macro-compartment" distinct from the remaining cytosol. Mutating three key surface lysine residues of HU nearly entirely abolished the weak and transitory interactions of HU with DNA and led to severe cell growth and DNA segregation defects, suggesting the importance of HU's interactions with chromosomal DNA mediated by the positively charged surface. A conserved proline residue important for recognizing bent and cruciform DNAs such as that in recombination intermediates, similarly abolished HU's rapid and transitory DNA interaction dynamics but had little impact on its apparent binding stability with nonspecific chromosomal DNAs. Interestingly, the proline residue appeared to be important for HUαβ dimer formation as mutating this residue makes HUαβ behave similarly to HUα2 dimers. Finally, we find that while prior evidence has found HU capable of depositing nucleoid-associated noncoding RNAs onto cruciform DNA structures, deletion of these specific naRNAs or inhibition of global transcription had a relatively minor effect on HU dynamics irrespective altered nucleoid compaction. Our results suggest a model of chromosome organization mediated by weak, transient interactions of HU, a substantial deviation from nucleoid-like proteins such as histones. Such collective sum of the numerous weak, transitory binding events of HU with nonspecific chromosome DNAs could generates a "force" to maintain a dynamic, fluid nucleoid with enough flexibility to rapidly facilitate global topological processes such as replication or nucleoid segregation.
- Downloaded 503 times
- Download rankings, all-time:
- Site-wide: 66,673
- In biophysics: 2,334
- Year to date:
- Site-wide: 117,860
- Since beginning of last month:
- Site-wide: 66,460
Downloads over time
Distribution of downloads per paper, site-wide
- 27 Nov 2020: The website and API now include results pulled from medRxiv as well as bioRxiv.
- 18 Dec 2019: We're pleased to announce PanLingua, a new tool that enables you to search for machine-translated bioRxiv preprints using more than 100 different languages.
- 21 May 2019: PLOS Biology has published a community page about Rxivist.org and its design.
- 10 May 2019: The paper analyzing the Rxivist dataset has been published at eLife.
- 1 Mar 2019: We now have summary statistics about bioRxiv downloads and submissions.
- 8 Feb 2019: Data from Altmetric is now available on the Rxivist details page for every preprint. Look for the "donut" under the download metrics.
- 30 Jan 2019: preLights has featured the Rxivist preprint and written about our findings.
- 22 Jan 2019: Nature just published an article about Rxivist and our data.
- 13 Jan 2019: The Rxivist preprint is live!