Ribosomal RNA and DNA
Because ribosomal RNA (rRNA) is present in large amounts in cells it is easily isolated. Because of its ease of isolation and because it plays a key role in protein synthesis, it and the genes that produce it (rDNA) have often been studied. Since it has a rather limited but essential function, it has remained relatively stable over evolutionary time. rRNA and rDNA have a short history in Paramecium, having been investigated in only a few laboratories from the late 1970s until the late 1990s. Now it is beginning to emerge again in its usefulness for studies on evolutionary biology. In Tetrahymena, however, it has been studied extensively by Meng-Chao Yao and his group, and they have made important additions to our knowledge of the molecular biology of that organism.