PIV, A FILAMENTOUS PHAGE PROTEIN THAT MEDIATES PHAGE EXPORT ACROSS THE BACTERIAL-CELL ENVELOPE, FORMS A MULTIMER

Filamentous phage pIV is an outer membrane protein required for phage assembly and secretion. Chemical cross-linking and sedimentation experiments have been used to demonstrate that pIV from f1-infected Escherichia coli exists as a homo-multimer, probably composed of 10 to 12 subunits. pIV secreted from spheroplasts remains soluble and does not form multimers.Synthesis of pIV from distantly related filamentous phages or from a bacterial homolog that participates in a specialized form of extra-cellular protein secretion in the same cell with pIV(f1) resulted in the formation of mixed multimers. This suggests that the homologous proteins themselves form homo-multimers. These structures could form gated channels that conduct assembling phage or specific substrate proteins across the outer membrane to the extracellular milieu. © 1994 Academic Press, Inc.