Mitochondrial RNA

Mitochondrial RNA (mRNA), which is distinct from RNA of nuclear origin, has been found in the mitochondrial function. The rate of lebelling of the mitochondrial fraction in vivo differs from that of RNA of a nuclear origin. A specific mitochondrial RNA polymerase is also strongly indicated.

Properties of MRNA and mitochondrial ribosomes.

1. MRNA is resistant to the action of ribonuclease. (Ribonuclease breaks down RNA of nuclear origin.
 
2. The ribosomes of mitochondria are probably 55-60S monomers. They are thus even smaller than bacterial ribosomes (70S). Three species of RNA have been isolated from yeast mitochondra, 23S, 16S and 4S. These values indicate that the ribosomes of yeast mitochondra are similar to the 70S bacterial ribosomes rather than to the 80S ribosomes of yeast and eukaryotes.

Synthesis of MRNA. It is now established that MRNA can be synthesized on a DNA template (presumably MDNA). DNA-dependent RNA polymerase has been demonstrated in rat-liver mitochondria.

Functions of MRNA. A complete protein synthesis mechanism is present in the mitochondrion. MDNA is capable of replication of means of the enzyme mitochondrial DNA polymerase. MDNA can also transcribe messenger MRNA by means of mitochondrial RNA polymerase. The MRNA then interacts with the ribosomes of the mitochondria and amino-acyl tRNA complexes, and protein is synthesized. Some MRNA is also of nuclear origin. This is indicated by the fact that certain regions of MRNA are complementary to nuclear DNA.