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 research outcomes extend past fundamental chemistry; they back up the notion that life originated in mineral- and sulfur-abundant settings like deep-sea hydrothermal vents. Such locations offered ideal circumstances for sulfur and metallic chemical reactions. Additionally, Professor Masel’s group discovered evidence indicating that earlier genetic mechanisms predate the common predecessor of all living organisms. This implies that early forms of life explored various methods to synthesize proteins prior to adopting the current known system.
To arrive at their findings, Professor Masel’s team categorized portions of proteins based on when they first emerged throughout evolutionary history. Known as domains, these segments perform distinct functions within cells. The scientists subsequently analyzed the frequency with which various types of amino acids occurred in both early and relatively recent protein groups. For instance, they discovered that glutamine might have been incorporated into the genetic code comparatively later than previously thought, challenging previous beliefs. Additionally, certain primeval proteins had unusually high concentrations of particular amino acids like tryptophan and tyrosine, suggesting different configurations in ancestral genetics that potentially functioned otherwise.
Professor Masel’s work provides not only fresh insights into Earth’s past but also potential avenues for exploring extraterrestrial life. The significance of sulfur- and metal-containing amino acids in early terrestrial life suggests these compounds may serve as indicators of life elsewhere in the cosmos. “Our findings enhance our understanding of the sequence in which the twenty amino acids became integrated into the genetic code,” explained Professor Masel, offering researchers a refined method to investigate the origins of life across different regions of the universe.
Journal Reference
Wehbi S., Wheeler A., Morel B., Manepilli N., Minh B.Q., Lauretta D.S., Masel J. “Sequence of amino acid incorporation into the genetic code determined through ancestral protein domains from the last universal common ancestor.” 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.