Unusual genetic code in Antarctic microbes yields rare amino acid, PgII

Key Highlights:

• A study published in Science reveals that certain archaea use the DNA sequence TAG to encode the rare amino acid pyrrolysine (Pyl), instead of signaling cells to stop protein synthesis.
• The discovery, led by researchers at the University of California, Berkeley, identifies a new genetic code, dubbed the 'Pyl code', with 62 sense codons and 21 amino acids.
• Researchers identified nine kinds of archaea where the TAG codon appeared to have been completely repurposed to encode Pyl, including Methanococcoides burtonii from Antarctic lakes and Methanomethylophilus alvi from the human gut.
• The study successfully modified Escherichia coli bacteria to express the archaeal cellular machinery required to read the Pyl code and incorporate Pyl in proteins.

Detailed Insights:

• The standard genetic code consists of 64 codons, with 61 encoding 20 common amino acids and 3 acting as 'stop' signals; exceptions to this universal code are rare, but this study highlights a significant one in certain archaea.
• The 'Pyl code' expands the known genetic dictionary, requiring scientists to rethink how they predict protein sequences for these organisms, interpreting all TAG codons as coding for Pyl for correct protein prediction.
• This finding has potential applications in bioengineering, allowing researchers to manipulate bacteria to produce useful materials by incorporating Pyl in proteins at desired positions.
• The study opens avenues for further research into the role of Pyl in proteins and whether its incorporation confers a fitness advantage to archaea in their natural environments.

Key Concepts Involved:

• Codon: A sequence of three DNA or RNA nucleotides that corresponds with a specific amino acid or stop signal during protein synthesis.
• Archaea: Single-celled microorganisms that are similar to bacteria in size and shape, but distinct in genetic makeup and biochemistry.
• Amino Acid: Organic compounds that are the building blocks of proteins, with each encoded by specific codons in the genetic code.