The genetic code, which controls how living things build proteins based on genetic instructions, may have developed in a different sequence than scientists once believed. A recent study explores the earliest stages of life and presents a new timeline for how the building blocks of proteins, called amino acids, were added to this code. This sequence is a key piece in the puzzle of how life first began.
Professor Joanna Masel and her colleagues from the University of Arizona introduced a new approach to figure out the order in which amino acids became part of the system that all life uses to make proteins. Their research, published in the scientific journal Proceedings of the National Academy of Sciences, avoids earlier guesses based on the chemicals found on early Earth. Instead, the team looked directly at the protein makeup of very old genetic material that dates back to the earliest known life forms.
Rather than relying on experiments that try to recreate early Earth conditions, Professor Masel’s team studied ancient genetic patterns likely shared by the very first organisms. These protein pieces are essential to many life processes and provide clues about how biology functioned billions of years ago. The researchers discovered that simpler, smaller amino acids were used first, while more complex ones came later. Surprisingly, types like methionine and cysteine, which include sulfur, and histidine, which interacts with metals, were added earlier than previously thought.
“Methionine and histidine were added to the code earlier than expected from their molecular weights, and glutamine later,” explained Professor Masel. This means methionine likely played a role in early energy-related processes, and histidine’s ability to help with metal-based chemical reactions may have made it crucial from the beginning.
The study’s findings go beyond basic chemistry. They support the idea that life began in environments rich in minerals and sulfur, such as underwater volcanic vents. These places would have provided the right conditions for sulfur and metal-based chemistry. Professor Masel’s team also found signs that some even older genetic systems existed before the earliest ancestor shared by all life, suggesting that life experimented with different ways to make proteins before settling on the system we know today.
To reach these conclusions, the Professor Masel’s team grouped protein parts by how far back in time they originated. These protein parts, called domains, are sections of proteins that carry out specific jobs in the cell. The researchers then compared how often each type of amino acid appeared in older versus slightly newer protein sets. They found, for example, that glutamine was likely added to the genetic code fairly late, overturning earlier assumptions. Other ancient proteins contained unusual amounts of specific amino acids, such as tryptophan and tyrosine, which hinted at older genetic arrangements that may have worked differently.
Professor Masel’s research offers more than a new view of Earth’s history. It also opens up possibilities for studying life beyond our planet. If sulfur and metal-based amino acids were important in early life here, they could be signs of life in other worlds too. “Our results offer an improved approximation of the order of recruitment of the twenty amino acids into the genetic code,” Professor Masel said, giving scientists a better way to trace how life might start in other parts of the universe.
Journal Reference
Wehbi S., Wheeler A., Morel B., Manepalli N., Minh B.Q., Lauretta D.S., Masel J. “Order of amino acid recruitment into the genetic code resolved by last universal common ancestor’s protein domains.” Proceedings of the National Academy of Sciences, 2024. DOI: https://doi.org/10.1073/pnas.2410311121
About the Author
Professor Joanna Masel is a theoretical biologist at the University of Arizona, known for her innovative work exploring how life’s most fundamental processes evolved. Her research focuses on the origins of genetic systems, evolutionary theory, and the molecular underpinnings of early life. With a background in mathematics and evolutionary biology, she bridges complex computational models with biological questions to uncover patterns that shaped life as we know it. Professor Masel has published widely on topics ranging from protein evolution to genetic robustness and the emergence of novel traits. Her work is recognized for challenging assumptions and providing new frameworks for understanding how biological systems adapt and evolve over time. Beyond her academic contributions, she is also a mentor and advocate for critical thinking in science, encouraging cross-disciplinary approaches to answer some of biology’s most difficult questions. Her recent work on amino acid recruitment offers a fresh perspective on how the genetic code may have first taken shape.
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