Schematic diagram of a nascent virion in the process of being secreted through the cell envelope. The outer membrane component of the channel, composed of a ring of 15 pIV subunits, is colored dark green. The front half of the outer membrane channel has been cut away in the image, in order to reveal the tight fit between the emerging virion and the interior of the channel. The inner membrane component of the channel, colored dark purple, is composed of pI and pXI subunits. A small N-terminal domain, N0, of each pIV subunit interacts with the inner-membrane component through a flexible linker (only two of the 15 N0 domains are depicted). As the nascent virion passes through the inner membrane, its DNA chromosome loses its cytoplasmic coat of phage pV subunits (light purple in the image) and acquires its sheath of coat proteins from the inner membrane. The chromosome is oriented with its packaging signal (hairpin [A] in Fig. 6) at the rounded tip. When the end of the chromosome is reached, five subunits each of minor coat proteins pIII and pVI are added to form the pointy tip of the virion. Adapted from Overview: Structure, Biology, and Applications of Filamentous Bacteriophages (Rakonjac et al. 2024) with permission from Cold Spring Harbor Laboratory Press.