Adaptor hypothesis
It was formulated by Francis Crick in 1955 in an informal publication of the RNA Tie Club, and later elaborated in 1957 along with the central dogma of molecular biology and the sequence hypothesis.
Crick postulated that there must exist a small molecule to precisely recognise and bind the mRNA sequences while amino acids are being synthesised.
[1] In their follow-up paper the same year, they introduced the concept of genetic information alongside the notion that DNA and protein cloud be related.
"[11] The correct interpretation of genetic information transfer (DNA → RNA → protein) developed by Crick in 1957 became the central dogma of molecular biology.
[18] Assuming that the four bases of DNA could produce 20 different combinations as triplets, he suggested that the different amino acids must correspond to a twenty-letter alphabet of the nucleotide sequence.
In a letter to Crick on 11 December 1954, discussing how RNA could be produced from DNA since they contain fundamentally similar nucleotide compositions, he wrote: "I suspect the answer is staring us in the face.
"[22] To solve the riddle of protein synthesis, Gamow (as the Synthesiser) created an informal team of scientists which he called the RNA Tide Club in 1954.
As his prediction to denote 20 amino acids, the club could have only 20 members, with the designated officers: Crick (as the Pessimist), Rich (the Lord Privy Seal) and Watson (the Optimist) among them.
The first was that he and Watson never had before counted the 20 amino acids or the possible 20 nucleotide triplets[19] (although Gamow was subsequently proven to be correct and his model was the first prediction of the genetic code[17][23]).
The adaptor hypothesis implies that the actual set of twenty amino acids found in proteins is due either to a historical accident or to biological selection at an extremely primitive stage.
[24] The template could consist of perhaps a single chain of RNA…Each adaptor molecule containing, say, a di- or trinucleotide would each be joined to its own amino acid by a special enzyme.
The lecture was further expanded and published as "On protein synthesis" in 1958, which science historian Horace Freeland Judson remarked: "The paper permanently altered the logic of biology.
Crick's thinking behind this proposal was based on a general consideration of the chemical properties of the two classes of molecule — nucleic acids and proteins.
By contrast, a nucleic acid is composed of a string of nucleotides whose sequence presents a geometrically defined surface for hydrogen bonding.
[29]As Crick was lecturing on his hypothesis, such adaptors do exist in nature was already discovered by the team of Mahlon Hoagland and Paul Zamecnik, whose paper was published the following year in March 1958.
