A model for proto-tRNA loading

Co-evolution of the genetic code and ribozyme replication

The origin of translation has stimulated much discussion since the basic processes involved were deciphered during the 1960s and 1970s. One strand of thought suggested that the process originated from RNA replication in the RNA world (Weiner & Maizels, 1987, 1994). In this paper I seek to extend this model. The mRNA originates as a replication intermediate of minus-strand ribozyme replication and thus contains all the genetic information contained in both the ribozyme portion and the putative tRNA-like portion of the RNA molecule. Qualitatively, this is similar to the model for the origin of chromosomes (Szathmary & Maynard-Smith, 1993, Maynard-Smith & Szathmary, 1993). This model explicitly describes the evolution of early chromosomes and the role replication played in generating the modern mRNA. Moreover, by pursuing this model, the START and STOP codons were derived and their original function with regard to the primitive 23S ribosomal RNA is suggested. Co-evolution of the genetic code (Wong, 1975) is also contained within the model. Lastly, I address some of the benefits and costs that the process may have for the organism in the context of autotrophy in the RNA world.

The emergence of life on Earth

Combined top-down and bottom-up research strategies and the principle of biological continuity were employed in an attempt to reconstruct a comprehensive origin of life theory, which is an extension of the coevolution theory (Lahav and Nir, Origins of Life Evol. Biosphere (1997) 27, 377-395). The resulting theory of emergence of templated-information and functionality (ETIF) addresses the emergence of living entities from inanimate matter, and that of the central mechanisms of their further evolution. It proposes the emergence of short organic catalysts (peptides and proto-ribozymes) and feedback-loop systems, plus their template-and-sequence-directed (TSD) reactions, encompassing catalyzed replication and translation of populations of molecules organized as chemical-informational feedback loop entities, in a fluctuating (wetting-drying) environment, functioning as simplified extant molecular-biological systems. The feedback loops with their TSD systems are chemically and functionally continuous with extant living organisms and their emergence in an inanimate environment may be defined as the beginning of life. The ETIF theory considers the emergence of bio-homochirality, a primordial genetic code, information and the incorporation of primordial metabolic cycles and compartmentation into the emerging living entities. This theory helps to establish a novel measure of biological information, which focuses on its physical effects rather than on the structure of the message, and makes it possible to estimate the time needed for the transition from the inanimate state to the closure of the first feedback-loop systems. Moreover, it forms the basis for novel laboratory experiments and computer modeling, encompassing catalytic activity of short peptides and proto-RNAs and the emergence of bio-homochirality and feedback-loop systems.