The translation systems of animal mitochondria are known to utilize extremely simplified tRNAs and rRNAs compared to the canonical translation systems of bacteria. It seems that the RNA deficit in mitochondrial systems has been accommodated by the selection for novel proteins and/or enlarged bacterial homologues with longer N- or C-terminal regions that compensate for the missing regions in animal mitochondrial RNAs. On the basis of our previous studies, we discuss the possibility that certain structures and functions of bacterial RNAs were transferred to proteins during the evolutionary process from ancestral to extant organisms. Our analyses may provide appropriate models for an experimental verification of the concept of transition from the "RNA world" to the "RNP world" in the early process of the evolution of life.