Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Study reveals new role for RNA interference during chromosomal replication

At the same time that a cell's DNA gets duplicated, a third of it gets super-compacted into repetitive clumps called heterochromatin.

This dense packing serves to repress or "silence" the DNA sequences within—which could wreck the genome if activated—as well as regulate the activity of nearby genes. When the cell divides, the daughter cells not only inherit a copy of the mother cell's DNA, but also the exact pattern in which that DNA is clumped into heterochromatin.

This "epigenetic" mode of inheritance—information not transmitted through the DNA code itself but by the way in which it is packaged—has long been investigated by Cold Spring Harbor Laboratory Professor and HHMI-GBMF Investigator Rob Martienssen. In a landmark study that was hailed as one of the breakthroughs of the year by Science magazine in 2002, Martienssen and his colleagues showed that the inheritance of heterochromatin depends on a set of mechanisms broadly defined as RNA interference (RNAi).

In a new study that appears online in Nature on October 16, Martienssen's team, including investigators from the Pasteur Institut in Paris and the University of Salamanca in Spain, describes a new role for RNAi, one that allows the DNA replication process itself to progress smoothly without resulting in DNA damage.

DNA is normally coiled around proteins called histones, which when chemically modified at specific locations, aggregate into dense arrays to form heterochromatin. Martienssen and others had previously found that RNAi guides this histone modification process, which occurs at the same time in the cell cycle when DNA is being duplicated.

In this RNAi-guided process, an enzyme called polymerase II copies or "transcribes" specific regions of DNA into RNA molecules, and somehow this modifies histones in those exact regions, thereby creating heterochromatin. These heterochromatic regions, however, alternate with so-called "origins of replication" – spots on the DNA where DNA-building proteins can bind, unzip the double-stranded DNA molecule to create a replication "fork," and begin to build a new strand of it.

This alternate arrangement of regions to be transcribed for heterochromatin assembly and regions that serve as origins for DNA replication raised a new question: how do the transcription machinery and the replication machinery work in tandem without colliding with each other and as a result stall the replication fork and trigger DNA damage?

In a recent study, Martienssen collaborated with scientists at the University of California at Berkeley and showed that the DNA-building proteins themselves could latch on to histone-modifying proteins and pull them along the replication fork.

"This finding raised the question of what role RNAi actually plays during the replication phase of the cell cycle," says Martienssen. "The answers to both questions turned out to be very simple and elegant."

His group's experiments in fission yeast, a simple model system used for studying heterochromatin, show that when the polymerase II enzyme has transcribed a stretch of DNA into RNA, the RNAi mechanism causes the enzyme to release its hold on the DNA and fall away. This allows the replication fork to progress smoothly and the DNA strands to be copied by the replication machinery. The histone-modifying proteins, which follow right along, establish heterochromatin.

The scientists found that failure or absence of the RNAi mechanism stalls replication, which triggers a strong "DNA damage" alert within the cell. That's when a repair mechanism called homologous recombination kicks in and repairs the stalled fork, but the ability to modify histones is lost.

"These experiments have revealed the real role of RNAi during the cell's replication phase, which is to protect cells from this sort of replication-associated fork damage," according to Martienssen.

"RNAi promotes heterochromatic silencing through replication-coupled release of RNA Pol II" appears online in Nature on October 16. The full citation is: Mikel Zaratiegui, Stephane Castel1, Danielle V. Irvine, Anna Kloc, Jie Ren, Fei Li, Elisa de Castro, Laura Marý´n, An-Yun Chang, Derek Goto, W. Zacheus Cande, Francisco Antequera, Benoit Arcangioli & Robert A. Martienssen. The paper can be downloaded at using the doi 10.1038/nature10501.

About Cold Spring Harbor Laboratory

Founded in 1890, Cold Spring Harbor Laboratory (CSHL) has shaped contemporary biomedical research and education with programs in cancer, neuroscience, plant biology and quantitative biology. CSHL is ranked number one in the world by Thomson Reuters for impact of its research in molecular biology and genetics. The Laboratory has been home to eight Nobel Prize winners. Today, CSHL's multidisciplinary scientific community is more than 350 scientists strong and its Meetings & Courses program hosts more than 11,000 scientists from around the world each year. Tens of thousands more benefit from the research, reviews, and ideas published in journals and books distributed internationally by CSHL Press. The Laboratory's education arm also includes a graduate school and programs for undergraduates as well as middle and high school students and teachers. CSHL is a private, not-for-profit institution on the north shore of Long Island. For more information, visit

Hema Bashyam | EurekAlert!
Further information:

More articles from Life Sciences:

nachricht When fat cells change their colour
28.10.2016 | Albert-Ludwigs-Universität Freiburg im Breisgau

nachricht Aquaculture: Clear Water Thanks to Cork
28.10.2016 | Technologie Lizenz-Büro (TLB) der Baden-Württembergischen Hochschulen GmbH

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel light sources made of 2D materials

Physicists from the University of Würzburg have designed a light source that emits photon pairs. Two-photon sources are particularly well suited for tap-proof data encryption. The experiment's key ingredients: a semiconductor crystal and some sticky tape.

So-called monolayers are at the heart of the research activities. These "super materials" (as the prestigious science magazine "Nature" puts it) have been...

Im Focus: Etching Microstructures with Lasers

Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.

This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...

Im Focus: Light-driven atomic rotations excite magnetic waves

Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion

Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Prototype device for measuring graphene-based electromagnetic radiation created

28.10.2016 | Power and Electrical Engineering

Gamma ray camera offers new view on ultra-high energy electrons in plasma

28.10.2016 | Physics and Astronomy

When fat cells change their colour

28.10.2016 | Life Sciences

More VideoLinks >>>