CSHL scientists discover link between control of chromosome duplication and s...( Cold Spring Harbor N.Y. Before a ce...),Health

Cold Spring Harbor, N.Y. Before a cell can divide into two, first it must duplicate its genetic material--the DNA packed in its chromosomes. The two new sets of chromosomes then have to be separated from one another and correctly distributed to the resulting "daughter" cells, so that both daughter cells are genetically identical to the original, or "parent," cell.

During cell division, a cellular organ called the centrosome, and a copy of the centrosome, position themselves at opposite ends of the dividing cell. Each centrosome serves as an anchor for a spindle, a complex structure of filament-like tubules that radiates out from each centrosome and connects with special sites called centromeres on the chromosomes. By pulling on the chromosomes, the spindles separate them into two sets, each divided equally into the two emerging daughter cells.

It's crucial that cells duplicate their centrosome only once during each division cycle. Extra copies can result in incorrect distribution of chromosomes, which can lead to genomic instability and cancer. Hence the importance of new research by Professor Bruce Stillman, Ph.D., and his lab group at Cold Spring Harbor Laboratory (CSHL). They have identified a protein molecule that controls the copying of the centrosome in human cells and prevents it from being re-duplicated. Their findings will appear in the February 6th issue of the journal Science.

Double duty for Orc1

The molecule shown by Dr. Stillman and his colleagues to control centrosome duplication is Orc1, one of six proteins that comprise the Origin Recognition Complex. ORC, as it is called, is an assembly that attaches to particular sequences within all the DNA in the cell and prepares it for duplication. Recently it had become clear that some ORC proteins might be doing more than jump-starting DNA duplication; the accumulation of extra centrosome copies in cells that lack ORC suggested that some or all
'/>"/>