Bacteriophage SPO1 structure and morphogenesis. II. Head structure and DNA size

Area of Science:

• Molecular Virology
• Structural Biology
• Bacteriophage Research

Background:

• Bacteriophage SPO1 is a model system for studying viral structure and DNA replication.
• Understanding capsid assembly and DNA packaging is crucial for viral infectivity.
• Previous studies have provided varying estimates for the SPO1 genome size.

Purpose of the Study:

• To elucidate the structural characteristics of the bacteriophage SPO1 capsid.
• To determine the precise size of the bacteriophage SPO1 double-stranded DNA genome.
• To investigate the structural consequences of mutations affecting capsid formation.

Main Methods:

• Electron microscopy was employed to analyze the icosahedral capsid structure and dimensions.
• Sedimentation analysis was used to determine the molecular weight of the SPO1 DNA.
• Mutational analysis of genes 5 and 8 was performed to study polyhead formation.

Main Results:

• The bacteriophage SPO1 capsid exhibits an icosahedral structure with a triangulation number (T) of 16 and a diameter of 87 nm.
• Mutations in genes 5 and 8 lead to the formation of tubular heads (polyheads) with a lattice constant of 13.4 nm and a diameter of 109.5 nm.
• The double-stranded SPO1 DNA, featuring 5' hydroxymethyl uracil, has a molecular weight of 86 x 10^6 (approximately 140 kilobase pairs), a revised and smaller estimate.

Conclusions:

• The study precisely defines the T=16 icosahedral capsid structure of bacteriophage SPO1.
• The formation of polyheads provides insights into capsid assembly mechanisms.
• A revised, smaller molecular weight for SPO1 DNA is reported, impacting future genomic studies.