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The role of the adsorption complex in the termination of filamentous phage assembly
V Gailus1, U Ramsperger, C Johner
1Fakultät für Biologie, Universität, Konstanz, Germany.
Abstract:
The adsorption complex of filamentous phage fd consists of two minor coat proteins, g3p and g6p, and is considered to be not only a structural entity, but also a functional unit to terminate phage assembly. Cells were infected with phage M13am8H1, which cannot assemble because it lacks the major coat protein g8p, although producing all of the other minor coat proteins. The membranes of infected cells were solubilized and analysed by non-denaturing PAGE and gel filtration. The data suggest the presence of the adsorption complex in these membranes. Furthermore, the non-polar gene 3 amber-mutant phage R171 was shown to lack g6p in the phage coat as well. The termination of assembly of this phage is disturbed, resulting in synthesis of polyphages. Electron micrographs and transient electrical birefringence show that these polyphages are eight times longer as compared to unit length phage. From these results, we conclude that the formation of the g3p-g6p complex is essential for correct termination of filamentous phage assembly.
Insights
The g3p-g6p complex is crucial for terminating filamentous phage assembly. Its absence leads to the formation of abnormally long polyphages, indicating its essential role in phage structure.
Area of Science:
- Molecular Biology
- Virology
- Structural Biology
Background:
- The filamentous phage fd adsorption complex, comprising minor coat proteins g3p and g6p, plays a role in phage assembly termination.
- Previous studies identified the adsorption complex as a structural and functional unit.
Purpose of the Study:
- To investigate the role of the g3p-g6p complex in the termination of filamentous phage assembly.
- To determine if the adsorption complex is present in infected cell membranes.
Main Methods:
- Infection of cells with specific phage mutants (M13am8H1 and R171).
- Solubilization and analysis of infected cell membranes using non-denaturing PAGE and gel filtration.
- Analysis of phage coat proteins.
- Electron microscopy and transient electrical birefringence to study phage morphology.
Main Results:
- Evidence for the presence of the adsorption complex in infected cell membranes.
- Demonstration that phage R171, lacking g6p, exhibits disturbed assembly termination.
- Observation of polyphages, eight times longer than unit length phage, in R171 infections.
Conclusions:
- The formation of the g3p-g6p complex is essential for the correct termination of filamentous phage assembly.
- The absence of this complex leads to the production of aberrant, elongated polyphages.