Abstract
To study the mechanism of heterochromatin formation in vertebrate cells, we isolated nuclei from chicken polymorphonuclear granulocytes and examined the chromatin organization. We found granulocyte chromatin to remain insoluble after nuclease digestion and to be resistant to swelling in low salt/high pH media. Both insolubility and resistance to swelling were lost after washing with 0.3 M NaCl, a procedure that released two abundant tissue-specific proteins from granulocyte nuclei. One of them (42 kDa) is identified as MENT, a protein previously shown to be associated with repressed chromatin from mature chicken erythrocytes. We show that MENT is immunolocalized in granulocyte heterochromatin, where it is one of the most abundant chromatin proteins ( approximately 2 molecules/200 base pairs of DNA). MENT is the first nuclear protein structurally related to the serine protease inhibitor family. The other abundant protein is similar to or identical with mim-1, a myeloid-specific protein that is known to be stored in cell granules and to associate with isolated nuclei. MENT (but not mim-1) binds chromatin and free DNA, and, at its physiological protein/DNA ratio, enhances compaction and the reversible Mg2+-dependent self-association of nucleosome arrays. MENT appears to promote the formation of heterochromatin by acting as a "glue" within and between chains of nucleosomes.
Highlights
In eukaryotic chromosomes, the DNA double helix is folded by proteins in a hierarchical manner
The demonstration that a developmentally regulated protein, MENT, accumulates in mature chicken granulocyte nuclei at a level sufficient to cause a total compaction of nuclear chromatin is one of the most significant results of this work
MENT is the first heterochromatin-associated protein shown to be capable of inducing chromatin structural transitions in vitro at its physiological protein/DNA ratio
Summary
A LINK BETWEEN TIGHT COMPACTION AND ACCUMULATION OF A HETEROCHROMATIN-ASSOCIATED PROTEIN (MENT)*. We observed that, in addition to the erythrocytespecific linker histone H5, the condensed and repressed chromatin from terminally differentiated chicken erythrocytes contained a 42-kDa polypeptide that was absent from the active chromatin fraction [16]. This protein, which was abundant in polymorphonuclear granulocytes, was designated as MENT (myeloid and erythroid nuclear termination stage-specific protein). Based on our studies of the interaction of purified MENT and mim-1 proteins with DNA and chromatin in vitro, we argue that it is the hyperaccumulation of MENT in chicken granulocyte nuclei that induces and maintains the high level of chromatin condensation in vivo. Chromatin remodeling during terminal differentiation in granulocytes may require only one major additional chromosomal protein (MENT)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
