In his lengthy letter Rich tried to demonstrate that he and his colleagues in his laboratory at the Massachusetts Institute of Technology had independently found many of the features of the model of phenylalanine transfer RNA of yeast that Aaron Klug was developing in Cambridge. Crick had accused Rich of using details of Klug's model without proper acknowledgement.. Crick had predicted the existence of transfer RNA in 1955 in his unpublished paper "On Degenerate Templates and the Adaptor Hypothesis," but separating, purifying, and making crystals of this group of unwieldy molecules (made up of 73 to 93 nucleotides) for X-ray diffraction study proved difficult and time-consuming. Robert Holley had sequenced the seventy-seven nucleotides of alanine transfer RNA of yeast in the mid-1960s, the first for any nucleic acid. A detailed model of the clover-leaf shaped three-dimensional structure of a transfer RNA, that of phenylalanine transfer RNA by Klug and his colleagues, was not completed until 1975.. NOTE: The margins are cut off in the original photocopied document.
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