= Nirenberg and Matthaei experiment
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In 1961, <Marshall Warren Nirenberg> and <J. Heinrich Matthaei> ground washed <Escherichia coli> and used <centrifugation> to prepare a <cell-free extract>. Reactions at $35^\circ\mathrm{C}$ combined <ribosomes>, soluble components, <ATP> regeneration and <phenylalanine> carrying a $^{14}\mathrm{C}$ <isotope> label, with or without <polyuridylic acid>, an <RNA> containing only U. After incubation, <trichloroacetic acid> <precipitation (chemistry)>, washing and counting <radioactive decay> detected label in insoluble material. Added <polyuridylic acid> strongly increased incorporation; removing <ribosomes> or <ATP> regeneration suppressed it. Product characterization supported a <phenylalanine> <polypeptide>.<The dependence of cell-free protein synthesis in E. coli upon naturally occurring or synthetic polyribonucleotides by Marshall Warren Nirenberg and J. Heinrich Matthaei>[pp. 1589–1590, Methods and Materials; p. 1592, Table 1 assay; pp. 1595–1600, Tables 6–9 and Figure 6]{ref}
\Image[/cell-free-polyuridylic-acid-decoding.png]
{title=<Nirenberg and Matthaei experiment>: preparation, comparison and readout}
{description=Original schematic; readout summarizes qualitative published observations.}
The inference connects an imposed <RNA> template to a specific <amino acid> product. Yet repeated U alone cannot distinguish one-, two- or three-letter coding units: every possible group still contains only U. Neither triplet length nor the complete <genetic code> follows.<The dependence of cell-free protein synthesis in E. coli upon naturally occurring or synthetic polyribonucleotides by Marshall Warren Nirenberg and J. Heinrich Matthaei>[p. 1601, Discussion and Note added in proof: coding-unit length not established]{ref}
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