Some oligonucleotides, alone or in association with other molecules, can exhibit enzymatic activity, which could have placed them at an advantage in competition for the most effective self-replication. Information gained by studying ribozymes, i.e. RNA molecules exhibiting enzymatic activity (Orgel 1986) is certainly very interesting in this respect. Most of the originally studied ribozymes are active in some area of processing RNA (Orgel 1986); nonetheless, at the present time, a great many ribozymes with a broad range of enzymatic activity are known (Connell & Christian 1993).
For example, the intron contained in the precursor of ribosomal RNA of the protozoa Tetrahymena thermophila is a typical ribozyme. This ribozyme is capable both of hydrolyzing various RNA-substrates, including its own pre-rRNA, and also of catalyzing the transfer of nucleotides from one nucleotide chain to another, i.e., reactions of the type
CpU + pGpN--> CpUpN + pG
where pU, pG and pN denote the 5’-monophosphate of the relevant nucleotide (N = U, C, A, G). In these reactions, the length of one nucleotide chain increases at the expense of another chain, so that they could be very useful in an environment in which competition occurs between various oligonucleotides. Ribozymes are considered by some biologists to be molecular relics of the time when there was, as yet, no division of functions between nucleic acids and proteins and when nucleic acids also performed all the functions that have been taken over by proteins in modern organisms.