<p>The PilT protein, N-terminal domain (PIN) is a compact domain of about 100 amino acids. The domain has two nearly invariant aspartates and forms a coiled-coil with other monomer units to polymerise a pilus fibre [<cite idref="PUB00006442"/>]. The function of the PIN domain is unknown but a role in signalling appears likely given the presence of this domain in some bacterial plasmid stability proteins and Dis3 from yeast that is implicated in mitotic control [<cite idref="PUB00001295"/>].</p>