G39P inhibits the initiation of DNA replication by blocking G40P replicative helicase. G39P has a bipartite stricture consisting of a folded N-terminal domain and an unfolded C-terminal domain. The C terminal is essential for helicase interaction [1].

1: Structural analysis of Bacillus subtilis SPP1 phage helicase loader protein G39P. Bailey S, Sedelnikova SE, Mesa P, Ayora S, Waltho JP, Ashcroft AE, Baron AJ, Alonso JC, Rafferty JB; J Biol Chem. 2003;278:15304-15312. PMID:12588876