Another function for the mitochondrial ribosomal RNA: Protein folding

Specialized proteins known as molecular chaperones bind transiently to non- native conformational states of proteins and protein complexes to promote t ransition to a biologically active conformation. Recently, it was demonstra ted in vitro that proteins do not uniquely possess this activity. We show t hat mitochondrial 12S and 16S ribosomal RNA can fold chemically denatured p roteins and reactivate heat-induced aggregated proteins in vitro. This chap erone action is ATP-independent. The specific secondary structure of the mi tochondrial rRNA is critical to its folding activity. Furthermore, mutant m itochondrial 16S rRNA from aged cardiac muscle cells lacked this activity. We propose that mitochondrial 12S and 16S ribosomal RNA may play an importa nt role in protein folding in mitochondria.