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Updated: Jan 8, 2026

Phage Phenomics: Physiological Approaches to Characterize Novel Viral Proteins
Published on: June 11, 2015
Structure of bacteriophage P1 head provides insight into capsid polymorphism
P1 myophage exhibits unique capsid polymorphism, with two distinct sizes (capsid_L and capsid_S). Specific protein appendages (DarA and Hdf) in larger capsids anchor viral DNA, influencing capsid morphogenesis.
Area of Science:
- Structural biology
- Virology
- Biochemistry
Background:
- P1 myophage capsid assembly is highly regulated, resulting in a unique polymorphism.
- Virions exist in two main capsid sizes: large (capsid_L, 95nm, T=13) and small (capsid_S, 68nm, T=7).
- Both capsid types share the same head protein with similar interactions.
Purpose of the Study:
- To investigate the structural differences and the role of protein appendages in P1 myophage capsid polymorphism.
- To understand the mechanism of dsDNA anchoring within different capsid sizes.
- To elucidate the contribution of specific proteins to capsid morphogenesis.
Main Methods:
- Comparative analysis of electron density maps of capsid_L and capsid_S.
- Examination of dsDNA content in relation to capsid size and protein appendages.
- Structural comparison of virion components.
Main Results:
- Protein appendages DarA and Hdf were identified below the 5-fold region in capsid_L, anchoring dsDNA.
- These densities were absent in capsid_S, correlating with reduced dsDNA packaging.
- Capsid_S, despite lacking significant dsDNA, retains essential genes for mature virion formation and shares structural components with capsid_L.
Conclusions:
- DarA and Hdf are crucial for dsDNA anchoring and play a significant role in P1 myophage capsid morphogenesis.
- The co-existence of two stable capsid conformations in a single lysate is a unique phenomenon.
- Capsid polymorphism in P1 myophage is linked to the presence or absence of specific DNA-binding protein appendages.
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