1963
Nirenberg and Tatum lead to 'cracking the code' of RNA. Using bacterial cells that they could make protein even when no intact living cells were present, they added an artifical form of RNA to the bacteria cells. The results of the addition caused it to make an unnatural protein composed entirely of the amino acid phenylalanine.
This provided the first clue to the 'code' through which RNA (and, ultimately, DNA) control the production of specific types of protein in the living cell.
Further experiments followed with other artificial mRNAs, but it was not then known how to make long artificial RNA chains with different bases in a particular order, so it was impossible to solve much of the code this way. However, Nirenberg and Leder found that RNA chains just three base units long (single codons, in effect), which could be made with bases in a specific order, would cause tRNA carrying the appropriate amino acid to stick fast to the ribosomes. These ribosomes were then filtered out, and the particular amino acid stuck to them could be determined by standard radioactive isotope techniques. The entire code was quickly broken down.
