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Pleiotropic effect of protein P6 on the viral cycle of bacteriophage phi29
1Centro de Biología Molecular "Severo Ochoa", Universidad Autónoma, Canto Blanco, 28049 Madrid, Spain.
Abstract:
The product of bacteriophage phi29 early gene 6, protein p6, is a double-stranded-DNA binding protein and one of the more abundant proteins during viral infection. We have studied the role of protein p6 in vivo through the infection of suppressor and nonsuppressor Bacillus subtilis strains with a phage carrying a nonsense mutation in gene 6, sus6(626). In the absence of functional protein p6, the two major processes of the viral cycle, transcription and DNA replication, were affected. Viral DNA synthesis was practically abolished, and early transcription was remarkably delayed and, in addition, underregulated at late times of the infection. The amount of protein p6 synthesized after infection with mutant phage sus6(626) under suppressor conditions was sixfold lower than that produced after wild-type infection. Nonetheless, phage production was as high as that obtained after wild-type infection. These results indicate that p6 is synthesized in amounts higher than those needed for most of its functions. However, the concentration of protein p6 appeared to be important for repression of the early promoter C2.
Insights
Bacteriophage phi29 protein p6 is crucial for viral DNA replication and transcription. Even at lower levels, p6 concentration is vital for repressing the early C2 promoter, ensuring efficient viral production.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Protein p6, encoded by bacteriophage phi29 early gene 6, is a double-stranded DNA-binding protein.
- It is highly abundant during viral infection, suggesting a significant role in the viral life cycle.
Purpose of the Study:
- To investigate the in vivo function of bacteriophage phi29 protein p6.
- To understand the impact of functional p6 absence on viral transcription and DNA replication.
Main Methods:
- Infection of Bacillus subtilis strains (suppressor and nonsuppressor) with a phi29 mutant phage (sus6(626)) lacking functional gene 6.
- Analysis of viral transcription, DNA synthesis, and phage production under different suppressor conditions.
Main Results:
- Absence of functional p6 abolished viral DNA synthesis and significantly delayed/underregulated early transcription.
- Lowered p6 synthesis under suppressor conditions did not impede phage production, indicating p6 is overproduced for some functions.
- Protein p6 concentration is critical for repressing the early C2 promoter.
Conclusions:
- Protein p6 plays essential roles in bacteriophage phi29 DNA replication and transcription regulation.
- While p6 is synthesized in excess of some functional requirements, its concentration is critical for efficient C2 promoter repression and overall viral propagation.