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Head morphologies in bacteriophage T4 head and internal protein mutant infections
Abstract:
Escherichia coli infected with phage T4 mutants defective in synthesis of the three major internal proteins found in the phage head, IPI-, IPII-, IPIII-, or IP degrees (lacking all three) were examined in the electron microscope for head formation. Infection with IPI- or IPII- does not appear to induce increased aberrant head formation, whereas IPII- or IP degrees infections result in production of polyheads and viable phage. Multiple mutants of the early head formation genes 20, 21, 22, 23, 24, 31, 40 and IP degrees were constructed. Combination with IP degrees increases polyhead formation when head formation is not blocked at a more defective stage but results in a qualitative shift to lump formation in association with gene 22 mutants. Thin-sectioning studies show morphologically similar cores in amber 21 and 21am IP degrees tau particles. These morphological observations, genetic evidence for interaction between ts mutants in gene 22 and the IP mutants, and analysis of the protein composition of tau particles further support the idea that p22 and the internal proteins form an unstable assembly core necessary for an early stage of head formation (M. K. Showe and L. W. Black, 1973).
Insights
Phage T4 mutants lacking internal proteins (IP) were studied for head formation. Mutations in internal proteins IPII- and IP degrees led to polyhead formation and viable phage, suggesting a role in early head assembly.
Area of Science:
- Molecular Virology
- Bacteriophage Genetics
- Structural Biology
Background:
- Bacteriophage T4 head formation is a complex process involving numerous genes.
- Internal proteins (IP) are crucial for the structural integrity and assembly of the phage head.
Purpose of the Study:
- To investigate the role of internal proteins (IP) in bacteriophage T4 head formation.
- To analyze the effects of specific IP mutants on aberrant head structures like polyheads.
Main Methods:
- Electron microscopy of Escherichia coli infected with various T4 phage mutants.
- Construction and analysis of multiple mutants affecting early head formation genes and IP.
- Thin-sectioning and protein composition analysis of phage tau particles.
Main Results:
- Mutants lacking IPI- or IPII- showed no significant increase in aberrant head formation.
- Infections with IPII- or IP degrees mutants resulted in polyhead production and viable phage.
- Combinations of IP degrees with early head gene mutants (e.g., gene 22) led to altered structures (lump formation) and supported the role of p22 and IPs in an assembly core.
Conclusions:
- Internal proteins, particularly in conjunction with gene 22 product (p22), are essential for forming a stable assembly core during early T4 phage head morphogenesis.
- Aberrant structures like polyheads and lumps are indicative of defects in this core assembly process.