Quantized viral DNA packaging revealed by rotating gel electrophoresis

Area of Science:

• Molecular Biology
• Virology
• Genetics

Background:

• Bacteriophage T4 uses a complex protein machinery to assemble its major head capsid.
• Head size and DNA packaging are critical for phage infectivity and genome integrity.
• Missense mutations in the T4 major head protein gene are known to affect head morphology.

Purpose of the Study:

• To investigate the relationship between mutations in the bacteriophage T4 major head protein gene and head length determination.
• To identify specific DNA length classes correlated with different head morphologies.
• To elucidate the regulatory mechanisms governing phage head length.

Main Methods:

• Analysis of bacteriophage T4 mutants with petite (pt) and petite and giant (ptg) missense mutations.
• Discontinuous rotating gel electrophoresis to resolve DNA from different phage particle types (petite, normal, giant).
• Correlation of DNA lengths with observed capsid structures.

Main Results:

• Two classes of mutations (pt and ptg) result in distinct head length phenotypes (normal, intermediate, isometric, and giant).
• Electrophoresis revealed distinct headful length DNA species corresponding to these phenotypes.
• Identified major DNA packaging stop points at Q = 13, 17, 21, and minor stop points at Q = 16, 18, 20.

Conclusions:

• Head length regulation in bacteriophage T4 is controlled by specific genetic mutations affecting the major head protein.
• The observed DNA length classes strongly correlate with capsid structure, suggesting a precise DNA packaging mechanism.
• A structural interaction between scaffold and capsid proteins likely dictates head length and, consequently, DNA length.