Structural basis for bacteriophage phi X174 assembly and eclipse as defined by temperature-sensitive mutations

Area of Science:

• Virology
• Molecular Biology
• Structural Biology

Background:

• Bacteriophage phi X174 is a model system for studying viral replication and assembly.
• Understanding the functions of viral genes is crucial for deciphering the viral life cycle.

Purpose of the Study:

• To develop and validate a screening procedure for classifying bacteriophage phi X174 temperature-sensitive (ts) mutants.
• To identify the specific genes and functions affected by these mutations.

Main Methods:

• Application of a novel screening procedure to 108 ts mutants.
• Quantitative one-step growth curve analysis.
• Genetic mapping of mutations.
• Analysis of amino acid substitutions within the atomic structure of wild-type (wt) virions.

Main Results:

• The screening procedure classified most mutants as defective in "late" functions (22/27).
• Mutations in "late" and "intermediate" classes primarily affected genes F, G, and H (structural proteins).
• Amino acid substitutions in F and G proteins suggest defects in protein-protein interactions during maturation and altered viral eclipse kinetics.

Conclusions:

• The F capsid protein plays a critical role in DNA ejection from the bacteriophage phi X174 capsid.
• The screening procedure effectively categorizes viral mutants, aiding in the study of viral mechanisms.
• Structural analysis of mutations provides insights into the molecular basis of viral assembly and function.