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The virion proteins encoded by bacteriophage phi K and its host-range mutant phi KhT: host-range determination and
1Molecular Biology Group, Faculty of Engineering, Toyama University.
Abstract:
The microvirid phage phi K, specific for Escherichia coli K12, contains a circular single-stranded (SS) DNA in the icosahedral virion, which comprises four phage gene products, F (capsid), G (major spike), H (minor spike), and J (core). phi KhT, a host-range mutant of phi K, can grow on E. coli C and B, besides K12, and is more thermosensitive than the parental phage phi K. Sequencing analysis revealed that the genome of phi K and phi KhT consists of 6,089 nucleotides (nt), and codes for eleven genes, whose sequences are similar to those of alpha 3, phi X174, and G4 infective to strain C. In phi KhT, two nt had changed: one is in the gene G, resulting in replacement of the 75th codon Ala with Ser, and the other is at 67th codon of the gene H: Val to Ala. Chemically synthesized gene J protein composed of 23 amino acids (aa) binds to phi K SS DNA more tightly than and preferentially over the host E. coli SS-DNA-binding protein (SSB). These results indicate that the two spike proteins G and H are involved in the determination of phi K host-range, and support a model in which the gene J protein functions in packaging the viral SS DNA into the virion vesicle.
Insights
The microvirid phage phi K
Area of Science:
- Microbiology
- Virology
- Molecular Biology
Background:
- The microvirid phage phi K infects Escherichia coli K12 and contains single-stranded DNA.
- Its genome is similar to other phages like alpha 3, phi X174, and G4.
- Phage phi K comprises four gene products: F (capsid), G (major spike), H (minor spike), and J (core).
Purpose of the Study:
- To investigate the genetic basis of host-range and thermosensitivity in phage phi K.
- To elucidate the function of phage phi K gene products, particularly G, H, and J proteins.
Main Methods:
- Genome sequencing of wild-type phi K and its mutant phi KhT.
- Site-directed mutagenesis analysis to identify genetic changes.
- Protein binding assays using chemically synthesized gene J protein.
Main Results:
- The genome of phi K and phi KhT consists of 6,089 nucleotides, encoding eleven genes.
- The host-range mutant phi KhT differs from phi K by two nucleotide changes in genes G and H.
- Synthesized gene J protein binds tightly and preferentially to phi K single-stranded DNA.
Conclusions:
- Phage phi K spike proteins G and H are crucial for determining host range.
- Phage phi K gene J protein plays a role in packaging viral single-stranded DNA into the virion.