Image from HERE.
From Today In Science History:
Today in 1953, Watson and Crick submitted to the journal Nature their first article on the structure of DNA, ”Molecular Structure of Nucleic Acids: A structure for deoxyribose nucleic acid”, which was published on April 25.
"We wish to put forward a radically different structure for the salt of deoxyribose nucleic acid. This structure has two helical chains each coiled around the same axis... Both chains follow right-handed helices... The novel feature of the structure is the manner in which the two chains are held together by purine and pyrimidine bases... They are joined together in pairs, a single base from one chain being hydrogen-bonded to a single base from the other chain, so that the two lie side by side with identical z-co-ordinates. One of the pair must be a purine and the other a pyrimidine in order for bonding to occur."