Structural and Functional Compensation by Proteins for the RNA Deficit of Animal Mitochondrial Translation Systems

Compared to the more usual bacterial translation systems, animal mitochondrial translation systems are unique in their use of extremely simplified RNAs. It seems that the RNA deficit of these mitochondrial systems is compensated by the presence of novel proteins and/or bacterial homologues that have longer N- or C-terminal regions, certain of which may compensate for missing regions in animal mitochondrial RNA. On the basis of two distinct cases 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.