Fig. 4.

Assembly pathway for the T4 DNA replication primosome. The primosome components are: gp41 subunits (blue ovals), gp61 subunit (red ellipse), GTP or GTPγS (yellow rectangles), and GDP (violet rectangle). The gp61 primase subunits are shown as elongated ellipsoids to reflect their higher frictional ratios compared with the relatively globular helicase subunits. The potential assembly pathways on the Right or Left of the figure lead to the formation of metastable aggregates, while the central pathway leads to a well-defined equilibrium complex with 6∶1 helicase to primase subunit stoichiometry, as shown by the included titration plots. For further details see text.