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Host and phi X 174 mutations affecting the morphogenesis or stabilization of the 50S complex, a single-stranded DNA
M C Ekechukwu1, D J Oberste, B A Fane
1Department of Biological Sciences, University of Arkansas, Fayetteville 72701, USA.
Abstract:
The morphogenetic pathway of bacteriophage phi X 174 was investigated in rep mutant hosts that specifically block stage III single-stranded DNA synthesis. The defects conferred by the mutant rep protein most likely affect the formation or stabilization of the 50S complex, a single-stranded DNA synthesizing intermediate, which consists of a viral prohead and a DNA replicating intermediate (preinitiation complex). phi X 174 mutants, ogr (rep), which restore the ability to propagate in the mutant rep hosts, were isolated. The org (rep) mutations confer amino acid substitutions in the viral coat protein, a constituent of the prohead, and the viral A protein, a constituent of the preinitiation complex. Four of the six coat protein substitutions are localized on or near the twofold axis of symmetry in the atomic structure of the mature virion.
Insights
Bacteriophage phi X 174 mutants were identified that can propagate in rep mutant hosts, overcoming defects in single-stranded DNA synthesis. These mutations alter viral coat and A proteins, impacting the 50S complex formation during morphogenesis.
Area of Science:
- Virology
- Molecular Biology
- Structural Biology
Background:
- Bacteriophage phi X 174 morphogenesis involves complex DNA replication intermediates.
- Rep proteins are crucial for stage III single-stranded DNA synthesis, a key step in viral assembly.
- Mutant rep hosts exhibit defects in forming the 50S complex, a viral DNA replication intermediate.
Purpose of the Study:
- To investigate the bacteriophage phi X 174 morphogenetic pathway in rep mutant hosts.
- To identify and characterize phi X 174 mutants that can overcome rep host defects.
- To understand the role of viral coat and A proteins in overcoming replication blockages.
Main Methods:
- Isolation and characterization of phi X 174 mutants (ogr) capable of propagation in rep mutant hosts.
- Genetic analysis of mutations conferring resistance to rep host defects.
- Mapping of amino acid substitutions within viral coat and A proteins.
Main Results:
- Isolation of phi X 174 ogr (rep) mutants that restore propagation in rep mutant hosts.
- Identification of amino acid substitutions in viral coat protein and A protein.
- Localization of four coat protein substitutions near the twofold symmetry axis of the mature virion.
Conclusions:
- Rep protein defects likely impair 50S complex formation or stabilization.
- Mutations in viral coat and A proteins can restore propagation by potentially compensating for rep defects.
- Structural analysis suggests coat protein substitutions may influence prohead stability or DNA interaction during morphogenesis.