Processing mitochondrial (t)RNAs: new enzyme, old job

While the principal mode of synthesis of the different human mitochondrial RNA species was recognized almost three decades ago, the constituents of one of the key players of the postulated RNA processing machinery were identified only recently. Human mitochondrial RNase P, the endonuclease responsible for tRNA 5' end maturation, turned out to be unlike any of its previously characterized cousins. It is not only devoid of the RNA moiety thought to be diagnostic of this type of enzymes so far, but it is instead built like a patchwork of multifunctional proteins coming together to moonlight in tRNA 5' end cleavage.