Baseplate conformational switch schematic reprinted from . A and B, The phage is free in solution. The long tail fibers are extended and oscillate around their midpoint position. The movements of the fibers are indicated with black arrows. The proteins are labeled with their corresponding gene numbers and colored as in other figures. C and D, The long tail fibers attach to their surface receptors and adapt the "down" conformation. The fiber labeled "A" and its corresponding attachment protein gp9 interact with gp11 and with gp10, respectively. These interactions, labeled with orange stars, probably initiate the conformational switch of the baseplate. The black arrows indicate tentative domain movements and rotations, which have been derived from the comparison of the two terminal conformations. The fiber labeled "B" has advanced along the conformational switch pathway so that gp11 is now seen along its threefold axis and the short tail fiber is partially extended in preparation for binding to its receptor. The thick red arrows indicate the projected movements of the fibers and the baseplate. E and F, The conformational switch is complete; the short tail fibers have bound their receptors and the sheath has contracted. The phage has initiated DNA transfer into the cell.