Through comparison among properties of nucleic acids, proteins, and oligo peptides, here I discuss RNA world and “first contact” between RNA and oligo peptide. From viewpoints of error rates in polymerization of those macromolecules, early systems were highly likely to have lower fidelity than present translation systems. Although such inaccurate synthesis may limit length of biopolymer, it also makes evolution easy by filling valleys in an activity landscape on a sequence space. Separation of information molecule and function molecule may contribute to fast evolution of genes by differentiation of fidelities in polymerization of those molecules.

Homochirality of proteins is essential for the development and maintenance of life. For a long time, it was considered that D-amino acids were excluded from living systems. However, recently D-aspartate (Asp) residues have been widely detected in proteins obtained from various tissues of elderly individuals. The presence of D-Asp in aged tissues of living organisms is a result of the spontaneous racemization of Asp residues during aging. This review deals with 1) the presence of D-Asp residues in protein of living tissues, 2) the mechanism of D-Asp formation in protein under physiological conditions, 3) the influence of D-Asp on protein structure and function 4) recent advances in D-amino acid analysis in protein.