The bacteriophage Mu middle operon: essential and nonessential functions.
Transcription during the bacteriophage Mu lytic cycle occurs in three phases: early, middle, and late. Previous DNA sequence analysis of the middle operon revealed five potential open reading frames (ORFs) with lengths of 39, 42, 72, 120, and 140 amino acids. The distal 140-amino-acid ORF encodes C, the activator of late transcription. Expression of the middle operon under the control of a T7 promoter and T7 RNA polymerase resulted in production of two polypeptides of 15 (ORF 120) and 16.5 kDa (C). Introduction of a linker containing a translation terminator into ORF120 resulted in the production of a truncated form of the ORF120 polypeptide. When the ORF120 linker mutation and several middle operon deletion mutations were assayed for their effect on Mu growth in Escherichia coli K12, the deletions caused 6- to 22-min delays in lysis, and two resulted in a smaller plaque morphology, but all gave normal plating efficiencies and burst sizes. The plating efficiencies for all the mutants were also similar to that of wild-type Mu on alternate hosts E. coli C, Citrobacter freundii, Shigella sonnei, and Shigella flexneri. These results indicate that, with the exception of C, the middle operon ORFs are not essential for phage development.
Department of Microbiology and Immunology, University of Tennessee at Memphis 38163.
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D000595:Amino Acid Sequence; D010583:Bacteriophage mu / Q000235:genetics*; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics; D002874:Chromosome Mapping; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D008565:Membrane Proteins / Q000235:genetics; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016366:Open Reading Frames / Q000235:genetics*; D009876:Operon; D033902:Periplasmic Binding Proteins; D010641:Phenotype; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D017386:Sequence Homology, Amino Acid; D014170:Transformation, Genetic; D014764:Viral Proteins / Q000096:biosynthesis / Q000235:genetics*
D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033902:Periplasmic Binding Proteins; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; C069968:fhuB protein, E coli