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Secondary and tertiary structural differences between histone H1 molecules from calf thymus and sea-urchin (Sphaerechinus granularis) sperm.

ABSTRACT: Tryptic digestion of histone H1 from the sperm of the sea urchin Sphaerechinus granularis leaves a limiting peptide of approx. 80 residues that is of similar size to the limit peptide from calf thymus H1 or chicken erythrocyte H5. The S. granularis limit peptide folds to form tertiary structure similar to that of the intact parent histone H1 (shown by n.m.r. spectra), but the helical content is decreased by the digestion from 64 residues to 28. In contrast, intact calf thymus H1 and chicken erythrocyte H5 histones have only about 28 helical residues, which are preserved in their limit peptides. The extra helix in S. granularis is shown to be rapidly digested away by trypsin, and its location in histone H1 is discussed. A possible relationship of this structural feature to the length of linker DNA is proposed.

SUBMITTER: Giancotti V

PROVIDER: S-EPMC1163177 | biostudies-other | 1981 Sep

REPOSITORIES: biostudies-other

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Project description:BackgroundLinker histone H1 has been studied in vivo and using reconstituted chromatin, but there have been few systematic studies of the effects of the cellular environment on its function. Due to the presence of many other chromatin factors and specific chaperones such as RanBP7/importin beta that regulate histone H1, linker histones likely function differently in vivo than in purified systems.Methodology/principal findingsWe have directly compared H1 binding to sperm nuclei in buffer versus Xenopus egg extract cytoplasm, and monitored the effects of adding nuclear import chaperones. In buffer, RanBP7 decondenses sperm nuclei, while H1 binds tightly to the chromatin and rescues RanBP7-mediated decondensation. H1 binding is reduced in cytoplasm, and H1 exhibits rapid FRAP dynamics in cytoplasm but not in buffer. RanBP7 decreases H1 binding to chromatin in both buffer and extract but does not significantly affect H1 dynamics in either condition. Importin beta has a lesser effect than RanBP7 on sperm chromatin decondensation and H1 binding, while a combination of RanBP7/importin beta is no more effective than RanBP7 alone. In extracts supplemented with RanBP7, H1 localizes to chromosomal foci, which increase after DNA damage. Unlike somatic H1, the embryonic linker histone H1M binds equally well to chromatin in cytoplasm compared to buffer. Amino-globular and carboxyl terminal domains of H1M bind chromatin comparably to the full-length protein in buffer, but are inhibited ?10-fold in cytoplasm. High levels of H1 or its truncations distort mitotic chromosomes and block their segregation during anaphase.Conclusion/significanceRanBP7 can decondense sperm nuclei and decrease H1 binding, but the rapid dynamics of H1 on chromatin depend on other cytoplasmic factors. Cytoplasm greatly impairs the activity of individual H1 domains, and only the full-length protein can condense chromatin properly. Our findings begin to bridge the gap between purified and in vivo chromatin systems.

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Secondary and tertiary structural differences between histone H1 molecules from calf thymus and sea-urchin (Sphaerechinus granularis) sperm.

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