Science / Medicine : Team Finds ‘Off’ Switch for Cellular Reproduction

Scientists at Stanford University School of Medicine reported last week in the journal Cell that they have found a chemical impulse that turns off a chromosome’s reproductive machinery in Escherichia coli, a common bacterium.

The start and finish of DNA synthesis are key processes in the life of a cell because they regulate how cells of embryos multiply and differentiate into all the varied organs that make life possible--lungs, hearts, brains, livers, blood and so forth. The same researchers found the start “signal” nearly a decade ago.

In normal cells the processes of replication stop when the cells reach adulthood. The discovery, said biochemist Arthur Kornberg, can eventually contribute to the understanding of many biological puzzles, including mutations, embryonic development and diseases such as cancer and AIDS. But Kornberg was quick to point out that, for the time being, the discovery is only a tool for further analysis of the code that tells a cell just when and how to start and stop duplicating.

“For the past nine years we have studied this biochemistry, and we now believe we have most of the molecules that operate the switch of replication in pure form,” Kornberg explained.