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Beads on a string: Discovering the nucleosome

University of Tennessee and ORNL researchers Ada and Don Olins discovered the nucleosome by electron microscopy in the 1970s, publishing their results in a 1974 issue of Science. Image credit: Ada Olins and Donald Olins, University of Tennessee/Oak Ridge Graduate School of Biomedical Sciences

75 years of science and technology

In the early 1970s, scientists at laboratories worldwide raced to unravel the mystery of how billions of miles of DNA are packaged inside the cells of the human body.

ORNL’s Don and Ada Olins were the first to discover the critical structure—the nucleosome—that winds DNA around proteins like thread around a spool.

The Olinses, a husband-and-wife research team in ORNL’s Biology Division and professors at the University of Tennessee–Oak Ridge Graduate

School of Biomedical Sciences, used electron microscopy to identify the nucleosome structures, describing them as “beads on a string.” This compact, orderly structure is at the heart of our genetic makeup as it forms the fundamental, repeating unit in chromosomes.

Capturing images of the nucleosomes and deducing their structure was no easy feat. The Olinses used an ORNL-developed method to study genetic material from chicken blood, rat liver and calf thymus with electron microscopy. They published ground-breaking micrographs in Science in 1974 along with a proposed nucleosome structure (a dyad particle, like

DNA, with pairs of basic proteins called histones) that was later confirmed.

The couple, who sign their communications with the apt shorthand “DnA,” continue to study these structures at the University of New England.

The discovery of the nucleosome revolutionized perceptions of DNA and DNA-related processes, including how genes are transcribed, replicated, repaired and expressed. It is a legacy that impacts research at ORNL today as scientists examine complex relationships among genes, the environment and physical traits, in fields as diverse as bioenergy and human health.