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The proteins of bacteriophage M13
Abstract:
Particles of the small filamentous coliphage M13 contain not only the major coat protein, which is the product of phage gene 8, but also a minor coat protein, the A protein, which is the product of gene 3. The A protein has a molecular weight of approximately 70,000 daltons, is present in one copy per virion, and is responsible for phage attachment to host cells. Also associated with purified M13 particles is a minor quantity of very small proteinaceous material, but its origin as a phage-coded product has not been demonstrated. At least five phage-specific proteins, including the two coat proteins, are present in appreciable quantities in M13-infected cells. The principal phage protein synthesized is the product of gene 5, which is responsible for phage single-stranded DNA synthesis. This protein has a molecular weight of about 8,000 daltons. Its precise function in DNA synthesis is not yet known. Phage proteins are synthesized at nearly normal rates in cells in which replication of phage double-stranded DNA is blocked by gene 2 mutations. This result suggests that the initial double-stranded DNA molecule serves as the principal template, perhaps the only template, for phage messenger RNA synthesis.
Insights
The M13 phage particle contains major and minor coat proteins, including the A protein for host attachment. Gene 5 product is key for single-stranded DNA synthesis, with initial double-stranded DNA acting as the primary mRNA template.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- The M13 phage is a small, filamentous bacteriophage.
- M13 phage particles are composed of major and minor coat proteins.
- The A protein (gene 3 product) is a minor coat protein crucial for M13 phage attachment to host cells.
Purpose of the Study:
- To characterize the protein composition of M13 phage particles.
- To identify phage-specific proteins synthesized during M13 infection.
- To investigate the role of M13 DNA replication in phage protein synthesis.
Main Methods:
- Analysis of M13 phage particle protein composition.
- Identification and quantification of phage-specific proteins in infected cells.
- Examination of protein synthesis in M13 mutants with blocked DNA replication.
Main Results:
- M13 phage particles contain major coat protein (gene 8) and A protein (gene 3).
- The A protein (approx. 70 kDa) is present in one copy per virion and mediates host cell attachment.
- The principal synthesized phage protein is the gene 5 product (approx. 8 kDa), essential for single-stranded DNA synthesis.
- At least five phage-specific proteins are found in M13-infected cells.
- Phage protein synthesis occurs at normal rates even when double-stranded DNA replication is blocked by gene 2 mutations.
Conclusions:
- The initial double-stranded M13 DNA molecule likely serves as the primary template for phage messenger RNA synthesis.
- The study elucidates the protein components of M13 phage and their roles in infection and replication.