Cold Spring Harbor, N.Y. 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 withinwhich could wreck the genome if activatedas 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 inheritanceinformation not transmitted through the DNA code itself but by the way in which it is packagedhas 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 replica
|Contact: Hema Bashyam|
Cold Spring Harbor Laboratory