The most unlikely pair of twins since Danny DeVito and Arnold Schwarzenegger just might be the daughter cells of the tiny Caulobacter crescentus bacterium. Caulobacter cells reproduce by giving rise to a pair of offspring -- one that swims and one that is rooted onto a stalk. The twins are different in other ways as well. The stalked twin immediately begins replicating its DNA in preparation for another cell division whereas the swimmer delays replicating its DNA until later in the cell cycle, after it sheds its flagellum and forms a stalk of its own. The Caulobacter crescentus study is part of a larger research program to better understand how cells regulate their growth and differentiation. Any disruption in these normal processes can eventually lead to cancer and other diseases. According to ONR Program Officer Eric Eisenstadt, understanding the architecture and logic of the cell's operating system could reveal new design principles for operating autonomous unmanned devices. In recently published reports, the Stanford researchers have determined that a "master regulator" protein prevents DNA replication from happening at the wrong time in the cell cycle. By carefully coordinating DNA replication with other events in the cell cycle, the Caulobacter ensures that each progeny cell, swarmer or stalked, ends up with the correct number of gene-bearing chromosomes. Recent research shows that the master regulator itself is controlled by processes within the cell.