James Watson: Astbury had the idea that a DNA molecule was a long linear molecule - where the bases
stacked on top of each other like piles of pennies.
The other thing we used was what Maurice Wilkins told us from the dimensions of the
crystalline form, there was clearly more than one chain in a nucleic acid molecule.
It was difficult to decide exactly how many because you had to measure the density
accurately, and that wasn't that simple, but he thought there was between two and
three. My recollection is that their preference was for three.
The other thing that we thought about was that since it crystallizes, it must be very
regular. But it was sort of our tenet that the sequence of bases along this molecule
were going to be irregular, and we thought they were going to be irregular because
we thought that's what would convey the genetic information. People now think that
was a great idea, but there was no other idea you could have. It was as simple minded
as it could be - if nucleic acids conveyed information, it was with the sequence of
the four bases.
Now, if they crystallize, well the bases being irregular, we thought, four different
types, four different shapes. That meant that the regular pattern must come from the
sugar-phosphate backbone. We thought that if there were several chains, and if they
pack together regularly to form crystal, then the sugar phosphate would have to be
in the center of the molecule.