The study of the primary structure of nucleic acids, i. e., the determination of the nucleotide sequence in ribosomal, transfer, and messenger types of RNA and in DNA, is an essential preliminary to the attempt to correlate the structures of these compounds with their functions. This is one of the most urgent problems in molecular biology, for until it is solved it is im possible to understand fully the mechanisms of fundamental living processes. Research has naturally tended to concentrate on the nucleic acids of smallest molecular weight, namely the transfer RNAs, and tremendous progress...