Plant mitochondrial RNase P and E. coli RNase P have different substrate specificities.

Substrate specificity requirements of the plant mitochondrial RNase P were investigated with different natural and mutated substrates. Heterologous precursors with intact tRNAs from plant and fungal mitochondria, from bacteria, archaebacteria and of eukaryotic origins were processed faithfully, albeit with different efficiencies. Alteration of the acceptor stem length did not disturb correct processing, while activity is completely inhibited by deletion of the pseudouridine loop. Such and other minimal substrates processed by the E. coli RNase P are not recognized as substrates by the plant mitochondrial enzyme, suggesting different requirements for substrate recognition.