Every healthy cell in the human body depends on tens of thousands of genes being switched on at precisely the right moment and in the right tissue. A long-standing mystery in molecular biology has been how the genome orchestrates this timing — specifically, how it recognizes the exact spot where a gene's instructions begin to be read. Now, researchers at the University of California San Diego have used artificial intelligence to decode the identity of one of the most important elements controlling that process: the 'initiator.'

The initiator is a short DNA sequence that marks the exact position where a gene starts to be expressed — converted from raw genetic instructions into functional proteins, enzymes, and other molecules. Despite its central role, the initiator's DNA pattern had never been fully decoded because of the enormous complexity involved.

In a study published in Genes and Development, graduate student Torrey Rhyne-Carrigg and colleagues in Professor James Kadonaga's lab used high-throughput DNA sequencing to measure gene expression activity across approximately 500,000 different versions of the initiator sequence. They then trained a machine learning model on that data to identify the characteristic DNA signature of a functional initiator.

Once the AI model had decoded that pattern, the team scanned the entire human genome and found that roughly 60% of human genes contain the initiator. The result reveals that this genetic 'on switch' is far more widespread than previously appreciated.

The practical implications are significant. With the initiator's DNA identity now known, researchers can scan for mutations in this region that might disrupt gene activation and contribute to diseases including cancer. The data and AI models could also support the design of synthetic promoters — engineered DNA sequences that switch genes on or off with customized functions — a capability with growing applications in gene therapy and synthetic biology.

Professor Kadonaga described the work as 'a step forward in the combined use of laboratory experiments and AI to decipher the information embedded in the DNA base sequence of humans.' He noted that within the six billion DNA base pairs in each human cell, there exists a gene expression code specifying when, where, and to what extent each gene should be activated. 'The new AI model for the initiator is a small but important part of this gene expression code,' he said, adding optimism that the team will expand their AI models of the full code in the near future.