Navigation Links
Scientists discover a genetic code for organizing DNA within the nucleus

DNA ?the long, thin molecule that carries our hereditary material ?is compressed around protein scaffolding in the cell nucleus into tiny spheres called nucleosomes. The bead-like nucleosomes are strung along the entire chromosome, which is itself folded and packaged to fit into the nucleus. What determines how, when and where a nucleosome will be positioned along the DNA sequence? Dr. Eran Segal and research student Yair Field of the Computer Science and Applied Mathematics Department at the Weizmann Institute of Science have succeeded, together with colleagues from Northwestern University in Chicago, in cracking the genetic code that sets the rules for where on the DNA strand the nucleosomes will be situated. Their findings appeared today in Nature.

The precise location of the nucleosomes along the DNA is known to play an important role in the cell's day to day function, since access to DNA wrapped in a nucleosome is blocked for many proteins, including those responsible for some of life's most basic processes. Among these barred proteins are factors that initiate DNA replication, transcription (the transfer of genetic information from DNA to RNA) and DNA repair. Thus, the positioning of nucleosomes defines the segments in which these processes can and can't take place. These limitations are considerable: Most of the DNA is packaged into nucleosomes. A single nucleosome contains about 150 genetic bases (the "letters" that make up a genetic sequence), while the free area between neighboring nucleosomes is only about 20 bases long. It is in these nucleosome-free regions that processes such as transcription can be initiated.

For many years, scientists have been unable to agree whether the placement of nucleosomes in live cells is controlled by the genetic sequence itself. Segal and his colleagues managed to prove that the DNA sequence indeed encodes "zoning" information on where to place nucleosomes. They also characterized this code and then, usin g the DNA sequence alone, were able to accurately predict a large number of nucleosome positions in yeast cells.

Segal and his colleagues accomplished this by examining around 200 different nucleosome sites on the DNA and asking whether their sequences have something in common. Mathematical analysis revealed similarities between the nucleosome-bound sequences and eventually uncovered a specific "code word." This "code word" consists of a periodic signal that appears every 10 bases on the sequence. The regular repetition of this signal helps the DNA segment to bend sharply into the spherical shape required to form a nucleosome. To identify this nucleosome positioning code, the research team used probabilistic models to characterize the sequences bound by nucleosomes, and they then developed a computer algorithm to predict the encoded organization of nucleosomes along an entire chromosome.

The team's findings provided insight into another mystery that has long been puzzling molecular biologists: How do cells direct transcription factors to their intended sites on the DNA, as opposed to the many similar but functionally irrelevant sites along the genomic sequence? The short binding sites themselves do not contain enough information for the transcription factors to discern between them. The scientists showed that basic information on the functional relevance of a binding site is at least partially encoded in the nucleosome positioning code: The intended sites are found in nucleosome-free segments, thereby allowing them to be accessed by the various transcription factors. In contrast, spurious binding sites with identical structures that could potentially sidetrack transcription factors are conveniently situated in segments that form nucleosomes, and are thus mostly inaccessible.

Since the proteins that form the core of the nucleosome are among the most evolutionarily conserved in nature, the scientists believe the genetic code they identifi ed should also be conserved in many organisms, including humans. Several diseases, such as cancer, are typically accompanied or caused by mutations in the DNA and the way it organizes into chromosomes. Such mutational processes may be influenced by the relative accessibility of the DNA to various proteins and by the organization of the DNA in the cell nucleus. Therefore, the scientists believe that the nucleosome positioning code they discovered may aid scientists in the future in understanding the mechanisms underlying many diseases.


'"/>

Source:American Committee for the Weizmann Institute of Science


Related biology news :

1. Scientists ID molecular switch in liver that triggers harmful effects of saturated and trans fats
2. Scientists Replicate Hepatitis C Virus in Laboratory
3. Scientists detect probable genetic cause of some Parkinsons disease cases
4. Scientists find missing enzyme for tuberculosis iron scavenging pathway
5. Scientists seek answers on what activates deadly anthrax spores
6. Yale Scientists Find MicroRNA Regulates Ras Cancer Gene
7. Scientists collaborate to assess health of global environment
8. Scientists decipher genome of fungus that can cause life-threatening infections
9. Scientists discover the cellular roots of graying hair
10. Scientists rid stem cell culture of key animal cells
11. Scientists develop new color-coded test for protein folding
Post Your Comments:
*Name:
*Comment:
*Email:


(Date:4/13/2017)... April 13, 2017 According to a new market ... Identity Analytics, Identity Administration, and Authorization), Service, Authentication Type, Deployment Mode, Vertical, ... Market is expected to grow from USD 14.30 Billion in 2017 to ... of 17.3%. ... MarketsandMarkets Logo ...
(Date:4/6/2017)... 2017 Forecasts by Product Type ... by End-Use (Transportation & Logistics, Government & Public Sector, ... Fossil Generation Facility, Nuclear Power), Industrial, Retail, Business Organisation ... Are you looking for a definitive report on the ... ...
(Date:4/3/2017)... 2017  Data captured by IsoCode, IsoPlexis ... a statistically significant association between the potency ... and objective response of cancer patients post-treatment. ... whether cancer patients will respond to CAR-T ... as to improve both pre-infusion potency testing and ...
Breaking Biology News(10 mins):
(Date:4/21/2017)... ... April 21, 2017 , ... The University of Connecticut, ... funding to three startups through the UConn Innovation Fund. The $1.5 million UConn ... affiliated with UConn. , The UConn Innovation Fund provides investments of up to ...
(Date:4/20/2017)... ... April 20, 2017 , ... As ... webinar will explore challenging patient cases when screening for direct oral anticoagulant. When ... be a need for bridging parental anticoagulation especially for those at high risk ...
(Date:4/20/2017)... , ... April 20, 2017 , ... NetDimensions appoints Bill ... , With over 20 years of experience in the learning technologies industry, Mastin joins ... company within Learning Technologies Group plc (LTG). At LEO, Mastin served as SVP of ...
(Date:4/20/2017)... , April 20, 2017 Dutch philosopher Koert van ... ,Next Nature, at the University of Technology in Eindhoven - has written ... this letter, he calls on humanity to avoid becoming a slave and victim ... ... Dutch philosopher Koert van Mensvoort – founder of the ...
Breaking Biology Technology: