Biologists' discovery may force revision of biology textbooks

August 18, 2011
Credit: James Kadonaga, UC San Diego

Basic biology textbooks may need a bit of revising now that biologists at UC San Diego have discovered a never-before-noticed component of our basic genetic material.

According to the textbooks, chromatin, the natural state of DNA in the cell, is made up of . And nucleosomes are the basic repeating unit of chromatin.

When viewed by a high powered microscope, nucleosomes look like beads on a string (photo at right). But in the August 19th issue of the journal Molecular Cell, UC San Diego biologists report their discovery of a novel chromatin particle halfway between DNA and a nucleosome (photo at left). While it looks like a nucleosome, they say, it is in fact a distinct particle of its own.

"This novel particle was found as a precursor to a nucleosome," said James Kadonaga, a professor of biology at UC San Diego who headed the research team and calls the particle a "pre-nucleosome." "These findings suggest that it is necessary to reconsider what chromatin is. The pre-nucleosome is likely to be an important player in how our is duplicated and used."

The say that while the pre-nucleosome may look something like a nucleosome under the microscope, biochemical tests have shown that it is in reality halfway between DNA and a nucleosome.

These pre-nucleosomes, the researchers say, are converted into nucleosomes by a motor protein that uses the energy molecule ATP (see graphic).

Credit: James Kadonaga, UC San Diego

"The discovery of pre-nucleosomes suggests that much of chromatin, which has been generally presumed to consist only of nucleosomes, may be a mixture of nucleosomes and pre-nucleosomes," said Kadonaga. "So, this discovery may be the beginning of a revolution in our understanding of what chromatin is."

"The packaging of DNA with to form chromatin helps stabilize and plays an important role in regulating gene activities and ," said Anthony Carter, who oversees chromatin grants at the National Institute of General Medical Sciences of the National Institutes of Health, which funded the research. "The discovery of a novel intermediate DNA-histone complex offers intriguing insights into the nature of chromatin and may help us better understand how it impacts these key cellular processes."

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3 / 5 (2) Aug 18, 2011
"And nucleosomes are the basic repeating unit of chromatin."

The basic building block of chromatin, the nucleosome, consists of 147 base pairs of DNA wrapped around a protein core of eight histones in a left-handed helical path of about one and a half turns [1,2].

There. Much better.

What is single, most important, all defining, difference between pre-nucleosomes and nucleosmes? The coil?

What is the exact molecular state and structure of the precursor to chromatin?

In the illustration:
What is the "particle" that is "new" and "discovered"?

What is the exact wording for new textbooks?

Due to character limit, the pending 45,000 associated questions to "...this novel particle..." must wait.

A retraction harbors the potential to make all 45,000 pending questions moot.

not rated yet Aug 23, 2011
I am inclined to agree. The article leaves a lot of detail to guess work. Not good. However the sequence needs to be explained in more detail to emphasise the order of hierachy of the particular pieces.

One thought did occur to me. What is to say that this 'new' structure isn't in fact a deformed nucleosome? After all there are so many toxins around that interfere with the creation of life that it is not beyond the realms of belief that this might well be the case.

Also the number of birth defects from the most miniscule amount of toxic pollutant is rapidly rising as we become more adept at discovering ever smaller particles and ever more diluted concentrations of the same.

I would be most interested to hear the outcome of this debate.

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