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Bacteriophage P22 virion protein which performs an essential early function. I. Analysis of 16-ts mutants
Abstract:
The product of gene 16 of phage P22, P16, is a head protein. P16 does not play an essential role in phage assembly since particles formed without this protein appear normal by electron microscopy examination (Botstein et al., 1973). P16 is essential when the particle infects a cell in the following cycle of infection (Botstein et al., 1973; King et al., 1973). We have characterized a mutant of P22 carrying a temperature-sensitive allele of gene 16. This mutant has previously been referred to as P22 25-ts (Levine et al., 1970, 1972) and P22 X-ts (Bezdek and Soska, 1970, 1973). P22 16-ts behaves as an early mutant at the nonpermissive temperature. Temperature shift experiments show that P16 of the infecting virion acts within the first 10 min at 25 C and that gene 16 product is required late in the latent period for incorporation into infectious phage. Induction does not require P16 for the production of particles. Particles produced either in a P22 16-ts thermal shift-up infection or after induction of 16-ts lysogens at 41 C are missing P16 and are, therefore, defective. P16 in P22 16-ts virions formed at the permissive temperature appears to be heat labile; it is inactivated after infection at 41 C. A simple assay for defective particles based on a complementation test is described.
Insights
The P22 phage gene 16 product (P16) is crucial for viral infection, not assembly. This study characterizes a temperature-sensitive P16 mutant, revealing its essential role early in infection and late in phage production.
Area of Science:
- Bacteriophage genetics
- Molecular virology
- Microbial pathogenesis
Background:
- Gene 16 product (P16) of bacteriophage P22 is a head protein.
- P16 is not essential for phage assembly but is critical for subsequent infection cycles.
- A temperature-sensitive mutant (P22 16-ts) of gene 16 was previously characterized.
Purpose of the Study:
- To characterize the P22 16-ts mutant.
- To determine the precise role and timing of P16 function during the phage life cycle.
- To develop an assay for defective phage particles.
Main Methods:
- Temperature shift experiments with P22 16-ts mutant.
- Analysis of phage particle production and infectivity under different temperature conditions.
- Complementation tests to assay for defective particles.
Main Results:
- P22 16-ts behaves as an early mutant at nonpermissive temperatures.
- P16 function is required within the first 10 minutes of infection at 25°C.
- P16 is also required late in the latent period for infectious phage production.
- Particles produced from temperature-shifted infections or induced lysogens are P16-deficient and defective.
- P16 in wild-type particles formed at permissive temperatures is heat-labile and inactivated upon infection at 41°C.
Conclusions:
- Gene 16 product (P16) plays a dual role: essential early in infection and late for progeny phage formation.
- The P22 16-ts mutant provides a tool to study P16 function.
- A complementation assay can identify P16-deficient, defective phage particles.