Probing intranuclear environments at the single-molecule level.

Citation data:

Biophysical journal, ISSN: 1542-0086, Vol: 94, Issue: 7, Page: 2847-58

Publication Year:
2008
Usage 18
Abstract Views 18
Captures 157
Readers 157
Citations 59
Citation Indexes 59
Repository URL:
https://escholarship.umassmed.edu/bmp_pp/173; https://works.bepress.com/david_grunwald/20
PMID:
18065482
DOI:
10.1529/biophysj.107.115014
PMCID:
PMC2267134
Author(s):
Grünwald, David; Martin, Robert M; Buschmann, Volker; Bazett-Jones, David P; Leonhardt, Heinrich; Kubitscheck, Ulrich; Cardoso, M Cristina
Publisher(s):
Elsevier BV
Tags:
Biochemistry, Genetics and Molecular Biology; Active Transport, Cell Nucleus; Animals; Cell Line; Cell Nucleus; Mice; Microscopy, Fluorescence; *Molecular Probe Techniques; Myoblasts; Streptavidin; Biochemistry; Biochemistry, Biophysics, and Structural Biology; Biophysics; Cell Biology; Molecular Biology
article description
Genome activity and nuclear metabolism clearly depend on accessibility, but it is not known whether and to what extent nuclear structures limit the mobility and access of individual molecules. We used fluorescently labeled streptavidin with a nuclear localization signal as an average-sized, inert protein to probe the nuclear environment. The protein was injected into the cytoplasm of mouse cells, and single molecules were tracked in the nucleus with high-speed fluorescence microscopy. We analyzed and compared the mobility of single streptavidin molecules in structurally and functionally distinct nuclear compartments of living cells. Our results indicated that all nuclear subcompartments were easily and similarly accessible for such an average-sized protein, and even condensed heterochromatin neither excluded single molecules nor impeded their passage. The only significant difference was a higher frequency of transient trappings in heterochromatin, which lasted only tens of milliseconds. The streptavidin molecules, however, did not accumulate in heterochromatin, suggesting comparatively less free volume. Interestingly, the nucleolus seemed to exclude streptavidin, as it did many other nuclear proteins, when visualized by conventional fluorescence microscopy. The tracking of single molecules, nonetheless, showed no evidence for repulsion at the border but relatively unimpeded passage through the nucleolus. These results clearly show that single-molecule tracking can provide novel insights into mobility of proteins in the nucleus that cannot be obtained by conventional fluorescence microscopy. Our results suggest that nuclear processes may not be regulated at the level of physical accessibility but rather by local concentration of reactants and availability of binding sites.