The products of gene I and the overlapping in-frame gene XI are required for filamentous phage assembly.
The class I filamentous bacteriophage are non-lytic single-stranded DNA phage, which are assembled at the cell envelope as they are extruded from the Gram-negative bacteria, Escherichia coli. The process requires the products of the phage genes I and IV, which reside in the inner and outer membrane, respectively, and are not present in the mature phage particle. Gene I encodes two proteins, the full length 348-residue pI and a smaller pI*, which this report shows is the result of an internal translation initiation event at methionine codon 241. Both pI and pI* are shown to be required for phage assembly. Therefore, pI* can be considered the product of an additional phage gene, XI, which is a separate in-frame gene that overlaps gene I. Both proteins contain a 13-residue region adjacent to the cytoplasmic face of the inner membrane that probably exists as a positively charged amphiphilic helix. Although this region is not required for membrane insertion of pI and pI*, it is shown to be required for phage assembly. Oligonucleotide-directed mutagenesis of this region, which removes positive charges or alters the hydrophobic face of the putative helix, renders pI and pI* unable to function in phage assembly. This region of pI and pI* is highly homologous in structure to the carboxyl-terminal 11 amino acids of pVIII, the main coat protein, which also reside adjacent to the cytoplasmic face of the inner membrane.
Rapoza
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MP
Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.
Webster
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D000595:Amino Acid Sequence; D001483:Base Sequence; D002462:Cell Membrane / Q000821:virology; D003090:Coliphages / Q000235:genetics / Q000502:physiology*; D003593:Cytoplasm / Q000821:virology; D004926:Escherichia coli / Q000821:virology; D015967:Gene Expression Regulation, Viral; D005807:Genes, Overlapping; D005814:Genes, Viral; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D014176:Protein Biosynthesis; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*; D014779:Virus Replication / Q000235:genetics*
D011993:Recombinant Fusion Proteins; D014764:Viral Proteins