DNA replication was in the hands of the biochemists, and they thought it was very straightforward, you just have an enzyme called DNA polymerase, which Arthur Kornberg had worked on and discovered, and you had DNA and you gave it some substrates and so you had the equation DNA plus DNA polymerase plus four triphosphates gives you more DNA. And that was the end of the story as far as the biochemists were concerned. But we were interested in... not in just copying DNA, but how this DNA would be segregated, given to daughter cells. Would you have to copy the DNA from many sites, which is what the biochemists had at least a picture of? And how would you regulate this? Because a bacterial cell copies DNA exactly once; takes the daughters, and segregates them to different cells. So our idea was that DNA replication started at one place. So that we had an element which later became the origin of replication. And that there was what we called positive regulation. Namely something had to appear which said start here and go on doing it. Now, the concept then was that it wouldn't matter about what DNA was attached to that unit, it would be just copied. As you… as you can see that later that became the whole basis of genetic engineering, because if a bacterial DNA could, so to speak, identify its own DNA as opposed to anything else you put into it, then that would have made all of this impossible, but we took the view DNA is DNA, it's just bases, and if you attach it to the right replication unit, then it will be copied willy-nilly and wouldn't require subsequent elements within it. And we proposed to test our hypothesis of positive regulation by a whole series of experiments, of which the very first one worked.