Visualization of G1 chromosomes: A folded, twisted, supercoiled chromonema model of interphase chromatid structure

Andrew S. Belmont, Kathy Bruce

Research output: Contribution to journalArticlepeer-review

Abstract

We have used light microscopy and serial thin-section electron microscopy to visualize intermediates of chromosome decondensation during G1 progression in synchronized CHO cells. In early G1, tightly coiled 100-130-nm 'chromonema' fibers are visualized within partially decondensed chromatin masses. Progression from early to middle G1 is accompanied by a progressive uncoiling and straightening of these chromonema fibers. Further decondensation in later G1 and early S phase results in predominantly 60-80- nm chromonema fibers that can be traced up to 2-3 μm in length as discrete fibers. Abrupt transitions in diameter from 100-130 to 60-80 nm along individual fibers are suggestive of coiling of the 60-80-nm chromonema fibers to form the thicker 100-130-nm chromonema fiber. Local unfolding of these chromonema fibers, corresponding to DNA regions tens to hundreds of kilobases in length, reveal more loosely folded and extended 30-nm chromatin fibers. Kinks and supercoils appear as prominent features at all observed levels of folding. These results are inconsistent with prevailing models of chromosome structure and, instead, suggest a folded chromonema model of chromosome structure.

Original languageEnglish (US)
Pages (from-to)287-302
Number of pages16
JournalJournal of Cell Biology
Volume127
Issue number2
DOIs
StatePublished - Oct 1994

ASJC Scopus subject areas

  • Cell Biology

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