The Function of the Hereditary Materials: Biological Catalyses Reflect the Cell's Evolutionary History

SYNOPSIS. The recent discovery of specialized RNA molecules that function like enzymes suggests that cells evolved before there were proteins. Such RNA-based cells would have contained large numbers of mutually supportive RNA molecules, each with a different catalytic function. Protein synthesis probably evolved later and was catalyzed by some of these RNA molecules. BecauseDNA must have been a relatively late addition to the cell, it is reasonable to assume that all DNA functions evolved in the presence of powerful protein catalysts.The above evolutionary perspective helps to explain why two different classes of catalytic mechanisms are used in present-day cells. The ancient processes of protein synthesis and pre-mRNA splicing are catalyzed by ribonucleoprotein particles, in which RNA catalysis still seems to play an important role. In contrast, late-evolving functions like. DNA replication are catalyzed by efficient protein machines. By analogy, protein machines are also likely to mediate the processes that control the transcription of eucaryotic genes.