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The bacteriophage Mu middle operon: essential and nonessential functions
1Department of Microbiology and Immunology, University of Tennessee at Memphis 38163.
Virology
|October 1, 1993
Summary
Bacteriophage Mu middle operon genes, except for the C activator, are not essential for phage development. Mutations caused lysis delays and altered plaque morphology but not overall growth efficiency.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Bacteriophage Mu lytic cycle transcription involves early, middle, and late phases.
- The middle operon contains five potential open reading frames (ORFs).
- The 140-amino acid ORF encodes C, the activator of late transcription.
Purpose of the Study:
- To investigate the function of bacteriophage Mu middle operon ORFs.
- To determine the essentiality of middle operon ORFs for phage development.
Main Methods:
- Expression of the middle operon using a T7 promoter and T7 RNA polymerase.
- Site-directed mutagenesis to introduce translation terminators into ORF120.
- Deletion mutagenesis of the middle operon.
- Assaying Mu growth and plaque morphology in Escherichia coli K12 and other hosts.
Main Results:
- Expression produced two polypeptides: 15 kDa (ORF 120) and 16.5 kDa (C).
- ORF120 mutations led to truncated polypeptide production.
- Middle operon deletions caused 6- to 22-minute lysis delays and altered plaque morphology.
- All mutants showed normal plating efficiencies and burst sizes across various hosts.
Conclusions:
- The middle operon ORFs, excluding C, are non-essential for bacteriophage Mu growth.
- The C protein is crucial for activating late transcription.
- Middle operon genes influence lysis timing and plaque morphology but not overall phage viability.