Maurice Wilkins by James Watson. During the second phase, 1951–52, Wilkins produced clear "B form" "X" shaped images from squid sperm, images he sent to James Watson and Francis Crick, causing Watson to write "Wilkins... has obtained extremely excellent X-ray diffraction photographs" [of DNA]. In 1953 Wilkins' colleague Rosalind Franklin instructed Raymond Gosling to hand over to Wilkins a high quality image of "B" form DNA ("Photo 51"), which she had made in 1952 but had “put it aside” as she was leaving King's College London. Wilkins showed it to Watson. This image, along with the knowledge that Linus Pauling had proposed
Non-helical models of DNA structure Natural Science, 7, (5), 85-100, 2018. The discovery of topoisomerases, enzymes that can change the linking number of circular nucleic acids and thus "unwind" the replicating bacterial chromosome, was largely seen by the mainstream scientific community to satisfy the topological objection to the Watson–Crick helical structure. The later X-ray crystallography data for the nucleosome, which showed a helical DNA structure wrapped around the protein nucleosome core particle, was considered to provide further affirmation for the existence of the helical structure "in vivo". Non-double-helical models are not currently accepted by the mainstream scientific community. Enzymes capable of unwinding and rewinding DNA