RNA world concept

Despite the current problems concerning RNA at the origin of life—in particular, the origin of the first RNA molecules and enzyme-free replication—the idea of an RNA world turned out to be a very useful concept. It initiated the search for molecular templates and created an entirely new field which may be characterized as template chemistry (Orgel, 1992). A series of systematic studies were performed, for example, on the properties of nucleic acids with modified sugar moieties (Eschenmoser, 1993). This studies revealed the special role of ribose and... 

However, DNA needs RNA to catalyze protein manufacture and it is now thought that RNA preceded DNA in molecular evolution. This has led to the concept of the "RNA world" (see Section 6.4, and Joyce, 1989, 2002). The RNA molecule has the capacity to both store information and to catalyze reactions, but unlike DNA it does not have the capacity to synthesize proteins. Nevertheless, it does... 

Ribosomal catalysis of peptide bond synthesis is mediated by regions of rRNA, and not by protein. Understand the implications of this catalysis for the concept of an RNA World. 

An additional rare form of RNA is the ribozyme (from nfeonucleic tnzyme). As the name implies, these are RNA molecules that have enzymic activity (Chap. 5). Many ribozymes catalyze the hydrolytic cleavage of RNA of either other RNA molecules or their own RNA. They are also an integral part of ribosomes where they have aminotransferase activity. The discovery of ribozymes, along with the realization that RNA can act as a hereditary molecule, gave rise to the concept by Leslie Orgel of an RNA world this idea posits that in the distant past, simple cells used RNA as structural, catalytic, and genetic elements (see Sec. 1.1). 

RNA copies of the genome would have directly acted as the chemical workhorses of this primitive life. This concept is known as the RNA world theory. 

Considering the basic principles of aptamer selection, the high potential of RNA to create a vast set of tertiary structures is conceivable from both the RNA world hypothesis [16] and the concept of molecular mimicry between RNA and protein [17]. We have created and characterized RNA aptamers against a variety of human proteins, including human translation initiation factors, immunoglobulin G (IgG), and human cytokines, as well as the cyanine dye Cy3, and these studies have contributed to our basic understanding of aptamer potential and global applications. 

An RNA aptamer has been selected to activate the carboxylic acid of amino acids that mimics the formation of a mixed phosphate anhydride synthesis of aminoacyl tRNA synthetases. The optimal aptamer requires only Ca + for the reaction, and operates at low pH with Xm 50 mM and /ccat 1.1 min for the activation of leucine. This lends support to the concept of translation in an RNA-based world. An RNA-cleaving DNAzyme has been used to target a chemokine receptor required by HIV-1 for entry into susceptible cells. The DNAzyme was found to be very efficient, and specifically interfered with the fusion of cells that harboured the T-lymphocytotropic HIV-1 envelope. 

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