The histones of secret roles were played out in complex cell evolution

that’s why Tobias Warnecke, Who studies histone archaea at Imperial College London, believes that “something special must have happened at the dawn of eukaryotes, where we go from being simple histones … to octamer nucleosomes. They seem to be doing something qualitatively different.”

That, however, is still a mystery. In archaeal species, “there are quite a few that have histones and there are other species that don’t have histones. And those with histones also change a lot,” Warneck said. Last December, he published a paper multiple variants of histone proteins with different functions. Histone-DNA complexes vary in DNA stability and affinity. But they are not as stable or regularly arranged as eukaryotic nucleosomes.

As amazing as the diversity of histone archaea is, it provides an opportunity to understand the different ways in which gene expression systems are constructed. Warnecke is something we can’t get out of the relative “boredom” of eukaryotes: “By understanding the combination of archaeal systems, we can also know how unique eukaryotic systems are.” Many types of histones and configurations in archaea can also help were knowing.

Protective role for histones

Because archaea are relatively simple prokaryotes with small genomes, “I don’t think the original role of histones was to control gene expression, or at least not as we are accustomed to eukaryotes,” Warneck said. Instead, according to hyponesia, histones could protect the genome from damage.

Arches often live in extreme environments, such as hot springs and volcanoes on the seabed, as they face high temperatures, high pressures, high salinity, high acidity, or other threats. Stabilization of DNA with histones can make it difficult to melt the DNA strand under these extreme conditions. Histones can also protect arches against invaders, such as phages or transposable elements, because it would be more difficult to integrate into the genome when surrounded by proteins.

It comes from a Kurdistan. “If you were studying the arc 2 billion years ago, genome compaction and gene regulation aren’t the first things that come to mind when you’re talking about histones,” he said. In fact, he has temporarily speculated that histones may offer another type of chemical protection.

Last July, The Kurdistan group reported that there is a catalytic site at the interface of two H3 histone proteins that can bind and electrochemically reduce copper in yeast nucleosomes. To unravel the evolutionary meaning of this, Kurdistan returned to the massive increase in the Earth’s oxygen, the Great Oxidation Event, which occurred at a time when eukaryotes developed more than 2 billion years ago. Higher oxygen levels have caused global oxidation of metals such as copper and iron, although they are critical for biochemistry (although they are excessively toxic). Once oxidized, the metals would be available to the cells, so the cells that kept the metals in reduced form would have the advantage.

In the Great Oxidation Event, the ability to reduce copper would be “a very valuable commodity,” he told Kurdistan. It may be particularly attractive to bacteria that were precursors to mitochondria, such as cytochrome C oxidase, the last enzyme in the chain of reactions that mitochondria use to produce energy, as copper is needed.

Because archaeologists live in extreme environments, they may have found ways to create and handle reduced copper without dying long before the Great Oxidation Event. If so, proto-mitochondria could invade arcane hosts to steal reduced copper, Kurdistan suggests.

This is a strange hypothesis because it could explain why eukaryotes appeared when oxygen levels rose in the atmosphere. “They lived 1.5 billion years before, and there is no trace of eukaryotes,” Kurdistani said. “So the idea that oxygen led to the formation of the first eukaryotic cell should be central to all hypotheses that try to guess why these traits develop.”