Ribosome evolution: Emergence of peptide synthesis machinery.

Proteins, the main players in current biological systems, are produced on ribosomes by sequential amide bond (peptide bond) formations between amino-acid-bearing tRNAs. The ribosome is an exquisite super-complex of RNA-proteins, containing more than 50 proteins and at least 3 kinds of RNAs. The combination of a variety of side chains of amino acids (typically 20 kinds with some exceptions) confers proteins with extraordinary structure and functions. The origin of peptide bond formation and the ribosome is crucial to the understanding of life itself. In this article, a possible evolutionary pathway to peptide bond formation machinery (proto-ribosome) will be discussed, with a special focus on the RNA minihelix (primordial form of modern tRNA) as a starting molecule. Combining the present data with recent experimental data, we can infer that the peptidyl transferase center (PTC) evolved from a primitive system in the RNA world comprising tRNA-like molecules formed by duplication of minihelix-like small RNA.

Conformational studies on nucleotide–amino acid interactions leading to origin of life.

Living processes may be defined as the self-sustained chemical reactions based on the special chemical machinery of nucleic acid-directed protein synthesis. Its genesis may be traced to the molecular interaction between nucleotides and amino acids leading to a primitive adaptor-mediated ordered synthesis of polypeptides. A primitive decoding system is described and its characteristics are shown to imitate, in a primitive manner, the present-day elaborate machinery of protein synthesis. This molecular interaction theory may be rightly considered as the missing link between the Protochemical and Biological Evolution. The origin of chiral specificity observed in living organisms is also traced to this specific molecular interaction in the protobiological milieu.