ABSTRACT
Sequencing of nucleic acids began in the 1960s, when the sequences of transfer RNAs (tRNAs) were determined. It was accomplished by methods that partially digested different portions of the RNA, and then the individual pieces were joined together on paper manually by the researchers. This was a painstaking process, so much so that the first RNA virus genomes were not fully determined until 1976 (for MS2, which is approximately 3.6 kb in length; Figure 21.1). Because most RNAs are single-stranded molecules, obtaining their sequences was limited to degradative methods at that time. However, at about the same time, DNA sequencing methods were developed, one using a degradative process and one using a polymerization reaction. The latter gained greater acceptance and was used initially for virus and organellar DNA sequencing projects, and eventually for projects on larger genomes, including those for Bacteria, Archaea, and Eukarya (including the initial human genome projects).
