5-Bromouracil: villian or hero? Mutagenesis with 5-bromouracil in bacteriophages

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Within genetics, 5-bromouracil plays dual roles - a genetic trickster and potential antiviral treatment. But how? The story begins with Watson and Crick who determined the structure of DNA in 1953. The base pairing between the four nucleotides ensures the stability of this structure and their specific sequence are the instructions of all life. However, mutagenic base analogs can disrupt this ordered sequence and lead to DNA mutations. 5-bromouracil is an analog of thymine and is formed by replacing the methyl group on the fifth carbon with bromine. The mutagenic properties of 5-bromouracil were first observed by the inhibition of growth in Lactobacillus casei bacteria when 5-bromouracil was added to the medium. This lay the foundations for Litman and Pardee who were determined to uncover 5-bromouracil’s mutagenic effects within bacteriophages.
In 1956, they conducted a groundbreaking experiment by growing E. coli bacteria in a medium containing sulphanilamide and 5-bromouracil. They then infected T2 bacteriophages into the medium and plated the culture at various concentrations of 5-bromouracil to determine if there was a concentration-dependant relationship. Notably, mutant plaques were revealed which were areas of bacterial cell death smaller than the wild-type plaques. Along with the confirmed concentration-dependant relationship, it was clear 5-bromouracil altered the viral genome by reducing the fitness and replication efficiency. The mechanism was hypothesised by Litman and Pardee to be competitive binding with thymine as they noticed sulphanilamide (which limits thymine synthesis) was essential for mutant plaque production. This was confirmed by multiple researchers who determined 5-bromouracil to exist in a keto form which binds with adenine and an enol form which binds with guanine. The tautomeric shifting results in A-T to G-C transitions during replication, significantly disrupting DNA structure and metabolism.
Emerging research shows the possibility for 5-bromouracil to be used in human antiviral medication and this was catalysed by Litman and Pardee’s experiment which provided evidence for the mutagenesis of 5-bromouracil in bacteriophages.
Creator: Isabella Atkinson
References:
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