Final answer:
To identify protein components involved in DNA synthesis, Nirenberg and Matthaei conducted cell-free protein synthesis experiments in E. coli. They added various cell fractions back together and found that one essential fraction contained RNA, which they substituted with a synthetic poly(U) preparation to synthesize proteins.
Step-by-step explanation:
In the classic paper by Nirenberg and Matthaei, they identified protein components involved in DNA synthesis by conducting cell-free protein synthesis experiments in E. coli. They isolated various cell fractions and added them back together along with amino acids and ATP as an energy source. They found that all four final sub-fractions must be added together to make radioactive proteins, and one of the essential cell fractions contained RNA that had been extracted from ribosomes. By substituting a synthetic poly(U) preparation for this fraction, they were able to synthesize proteins with a simple repeating amino acid.