Featured Research

from universities, journals, and other organizations

Essential Cell Division "Zipper" Anchors To So-Called Junk DNA

Date:
August 30, 2002
Source:
The Wistar Institute
Summary:
When cells divide in two, they must carefully manage the process by which their DNA is replicated and then apportioned to the daughter cells. In one critical step along the way, the replicated DNA strands - or sisters - are held together for a period by a temporary scaffold of bridging proteins. When the timing is right, the proteins unzip, allowing the DNA sisters to separate. Errors in this or other steps in cell division can lead to cell death, faulty development, or cancer, which is largely defined as misregulated cell division.

PHILADELPHIA - When cells divide in two, they must carefully manage the process by which their DNA is replicated and then apportioned to the daughter cells. In one critical step along the way, the replicated DNA strands - or sisters - are held together for a period by a temporary scaffold of bridging proteins. When the timing is right, the proteins unzip, allowing the DNA sisters to separate. Errors in this or other steps in cell division can lead to cell death, faulty development, or cancer, which is largely defined as misregulated cell division.

Scientists have had a number of questions about these important bridging proteins, called cohesins. For example, how and where do the proteins attach themselves to the DNA? To protect genes from inappropriate activation, DNA is tightly wrapped around small proteins called histones and then further coiled into a higher structure called chromatin that serves as an effective accessibility barrier to the genes.

In a new study in the August 29 issue of Nature, researchers at The Wistar Institute identify a cohesin-containing protein complex that reshapes chromatin to allow cohesins to bind to DNA. In doing so, they also identified the locations on the human genome where the cohesins bind. Somewhat to their surprise, the binding sites were found to be a repetitive DNA sequence found throughout the human genome for which no previous role had ever been identified. These bits of DNA, known as Alu sequences, are liberally represented along those vast stretches of the human genome not known to directly control genetic activity, sometimes referred to as junk DNA.

"One thing that interested us is that there are 500 thousand to 1 million Alu repeats across the human genome," says Ramin Shiekhattar, Ph.D., an associate professor at The Wistar Institute and senior author on the Nature study. "These sequences are very common. And this makes sense if one of their roles is to bind to the bridging proteins, the cohesins, to keep the replicated DNA sisters together until it is time for them to separate. Multiple bridging sites throughout the DNA would be needed for this system to work. They couldn't be unique sequences."

In their investigations, Shiekhattar and his coworkers noticed that many, but not all the Alu sequences bound cohesin, and they wondered what rules might govern the process. Additional experiments revealed that if the histone proteins were methylated and acetylated - that is, if a methyl and acetyl molecule were bound to them - then the chromatin structure relaxed to allow access to the DNA. But if the Alu sequence on the DNA was itself methylated, then the cohesin could not bind to the DNA at that site.

Why these modifications might take place at some Alu sites and not others was not clear. But, taken together, the research team's observations are supportive of the existence of what some scientists have termed a "histone code." This recently proposed theory suggests that a system of complex, interdependent modifications to histones is responsible for regulating access to DNA and genes.

"The idea that a kind of code of modifications to the molecular packaging of DNA may govern gene activity is an intriguing one," Shiekhattar says. "If we were to better understand this code, it might provide us with important insights into diseases tied to problems in gene control, including developmental disorders and cancer. These are some of the questions we're looking into now, using this study as a starting point."

The lead author on the Nature study is Mohamed-Ali Hakimi, Ph.D., at The Wistar Institute. The other Wistar-based coauthors are Daniel A. Bochar, Ph.D., Yuanshu Dong, and Orr G. Barak. Wistar professor David W. Speicher, Ph.D., collaborated on the study, as did John A. Schmiesing, Jr., and Kyoko Yokomori at the University of California, Irvine. This research was supported by a grant from National Institutes of Health.

The Wistar Institute is an independent nonprofit biomedical research institution dedicated to discovering the causes and cures for major diseases, including cancer, cardiovascular disease, autoimmune disorders, and infectious diseases. Founded in 1892 as the first institution of its kind in the nation, The Wistar Institute today is a National Cancer Institute-designated Cancer Center - one of only eight focused on basic research. Discoveries at Wistar have led to the development of vaccines for such diseases as rabies and rubella, the identification of genes associated with breast, lung, and prostate cancer, and the development of monoclonal antibodies and other significant research technologies and tools.


Story Source:

The above story is based on materials provided by The Wistar Institute. Note: Materials may be edited for content and length.


Cite This Page:

The Wistar Institute. "Essential Cell Division "Zipper" Anchors To So-Called Junk DNA." ScienceDaily. ScienceDaily, 30 August 2002. <www.sciencedaily.com/releases/2002/08/020830072103.htm>.
The Wistar Institute. (2002, August 30). Essential Cell Division "Zipper" Anchors To So-Called Junk DNA. ScienceDaily. Retrieved July 23, 2014 from www.sciencedaily.com/releases/2002/08/020830072103.htm
The Wistar Institute. "Essential Cell Division "Zipper" Anchors To So-Called Junk DNA." ScienceDaily. www.sciencedaily.com/releases/2002/08/020830072103.htm (accessed July 23, 2014).

Share This




More Health & Medicine News

Wednesday, July 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Courts Conflicted Over Healthcare Law

Courts Conflicted Over Healthcare Law

AP (July 22, 2014) Two federal appeals courts issued conflicting rulings Tuesday on the legality of the federally-run healthcare exchange that operates in 36 states. (July 22) Video provided by AP
Powered by NewsLook.com
Why Do People Believe We Only Use 10 Percent Of Our Brains?

Why Do People Believe We Only Use 10 Percent Of Our Brains?

Newsy (July 22, 2014) The new sci-fi thriller "Lucy" is making people question whether we really use all our brainpower. But, as scientists have insisted for years, we do. Video provided by Newsy
Powered by NewsLook.com
Scientists Find New Way To Make Human Platelets

Scientists Find New Way To Make Human Platelets

Newsy (July 22, 2014) Boston scientists have discovered a new way to create fully functioning human platelets using a bioreactor and human stem cells. Video provided by Newsy
Powered by NewsLook.com
Gilead's $1000-a-Pill Drug Could Cure Hep C in HIV-Positive People

Gilead's $1000-a-Pill Drug Could Cure Hep C in HIV-Positive People

TheStreet (July 21, 2014) New research shows Gilead Science's drug Sovaldi helps in curing hepatitis C in those who suffer from HIV. In a medical study, the combination of Gilead's Hep C drug with anti-viral drug Ribavirin cured 76% of HIV-positive patients suffering from the most common hepatitis C strain. Hepatitis C and related complications have been a top cause of death in HIV-positive patients. Typical medication used to treat the disease, including interferon proteins, tended to react badly with HIV drugs. However, Sovaldi's %1,000-a-pill price tag could limit the number of patients able to access the treatment. TheStreet's Keris Lahiff reports from New York. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins