A forward mutation assay in phage T4: application to gene 42 mutator mutations

Area of Science:

• Molecular Biology
• Genetics
• Virology

Background:

• Bacteriophage T4 gene 42 encodes deoxycytidylate hydroxymethylase, crucial for DNA synthesis.
• Temperature-sensitive alleles can be used to probe enzyme function and mutagenesis.
• Understanding mutagenic specificity is key to deciphering DNA repair and replication processes.

Purpose of the Study:

• To develop and utilize a forward mutation assay for studying mutagenic specificity.
• To investigate mutations induced by temperature-sensitive alleles of bacteriophage T4 gene 42.
• To analyze the sequence context and neighboring nucleotides influencing mutation types.

Main Methods:

• Development of a forward mutation assay using bacteriophage T4.
• Selection of thymidine kinase (tk) mutations induced by T4 ts B3 at a semi-permissive temperature.
• PCR amplification of the tk gene and DNA sequencing of identified mutations.

Main Results:

• The assay identified primarily C-->T transitions (21/23 mutations) and some C-->A transversions.
• Analysis suggests that the mispairing of thymine with guanine is suppressed by the presence of dGTP.
• The 5' neighbor nucleotide influences mutation frequency, with no observed mutations adjacent to dAMP.

Conclusions:

• The forward mutation assay is effective for studying mutagenic specificity in T4 phage.
• The mutator phenotype of T4 ts B3 is linked to impaired deoxycytidylate hydroxymethylase activity affecting dNTP pools.
• The findings support a model where nucleotide pool imbalances drive mutagenesis.