The Scientist November 2019

TWO GENOMES, ONE CELL

For 1.5 billion years, the mitochondrial and nuclear genomes have been coevolving. Over this time, the mitochondrial genome became
reduced, retaining only 37 genes in most animal species, and growing reliant on the nuclear genome to fulfi ll the organelle’s primary func-
tion—to produce AT P by oxidative phosphorylation. Mitochondrial gene products interact with those encoded in nuclear genes, and
sometimes with the nuclear genome itself. Because the mitochondrial genome mutates faster than the nuclear genome, it takes the lead
in the mitonuclear evolutionary dance, while the nuclear genome follows, evolving compensatory mutations to maintain coadapted gene
complexes. Researchers are now coming to appreciate that this has consequences for physiology and even macroevolution.

NUCLEUS

MITOCHONDRIA

nDNA

Cytochrome

oxidase

Mitochondrion-

encoded

component

Nucleus-enconded

component

Amino

acid

tRNA

aaRs

LUCY

READING-IKKANDA

COMPOSITE PROTEINS

Researchers have long known that many

proteins are made of several compo-

nents, some of which are coded for in

the mitochondrial genome, and others

being coded for in the nuclear genome.

Cytochrome oxidase, the last enzyme in

the respiratory electron transport chain,

is one example.

NUCLEAR GENE EXPRESSION

Mitochondrial gene products can infl uence the

expression of nuclear genes, though the mechanisms

are as yet unclear.

MITOCHONDRIAL FUNCTION

Mitochondria require nuclear gene

products to continually produce energy

for the cell. For example, mitochondrial

protein translation requires aminoacyl

tRNA synthetases (aaRS) encoded by

the nuclear genome to attach amino

acids to the corresponding tRNAs

encoded by the mitochondrial genome.

?