Large Scale Chromatin Structure

Division Of Basic Sciences - Nci

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Abstract

Large-scale chromatin structure is the higher-order folding of chromatin on the scale of several hundred kilobases. Little is known about this folding, but the structures must influence transcription, replication and repair of DNA. To learn more about these structures, we previously examined transcriptionally active domains of 400 - 2000 kb by light microscopy. We found that several different domains exhibit similar structures in light microscope images, namely a series of adjacent puncta or "beads" approximately 0.5 microns in diameter. When these same domains are transcriptionally inactive, only one punctum or "bead" is detected. Thus transcription induces a decondensation from single beaded to multi-beaded structures. To observe these structures at higher resolution we are exploring the applicability of x-ray microscopy. This imaging modality enables visualization of whole, unsectioned mammalian cells at 25 nm resolution. Detection of chromatin relies on the natural contrast afforded by the absorption of organic matter relative to water. Our goal is to determine if chromatin structure can be detected by this approach and if so, then to provide a 3D image of nuclear chromatin at 25 nm resolution.