Pathways of thymidine hypermodification

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Bacterial viruses (bacteriophages) possess unique DNA modifications, particularly to thymidine, serving as a defense mechanism against host endonucleases.
• The biosynthetic origins of these complex thymidine modifications remain largely unknown.
• Many bacteriophages, such as Pseudomonas phage M6 and Salmonella phage ViI, feature extensive post-replicative modifications of 5-hydroxymethyluridine (5-hmdU).

Purpose of the Study:

• To elucidate the biosynthetic pathways responsible for thymidine hypermodifications in bacteriophage DNA.
• To identify the source of chemical diversity in these DNA modifications.
• To explore the potential for novel DNA modification chemistry in viral metagenomes.

Main Methods:

• Analysis of thymidine modifications in bacteriophage DNA.
• Enzymatic assays to determine the installation of amino acids onto 5-hmdU.
• Identification of enzyme classes involved in sculpting appended amino acids (e.g., radical SAM isomerases, PLP-dependent decarboxylases, flavin-dependent lyases, acetyltransferases).
• Bioinformatic analysis of viral metagenomes to assess the diversity of modification genes.

Main Results:

• Thymidine hypermodifications in bacteriophages are derived from free amino acids enzymatically installed on 5-hmdU.
• A variety of enzyme classes further modify these appended amino acids, creating diverse chemical structures.
• Viral metagenomes reveal a wide array of thymidine hypermodification genes, suggesting extensive chemical diversity.

Conclusions:

• The study reveals that amino acids are key building blocks for complex DNA hypermodifications in bacteriophages.
• Enzymatic sculpting of these amino acids leads to a rich diversity of chemical structures.
• The vast genetic diversity of DNA hypermodifications in viral metagenomes represents a significant, untapped reservoir of novel chemical entities.