HelP is required for ICEBs1 transfer and replication.

Mating efficiencies and copy numbers (averages from at least 3 independent experiments ± standard deviation) were measured one hour after induction of ICEBs1 gene expression by overproduction of RapI from amyE::{Pspank(hy)-rapI spc}. Copy number of oriT is expressed relative to a control region ydbT adjacent to ICEBs1. Wild type and all derivates of ICEBs1 contained Δ(rapI-phrI)::kan. The ICEBs1 constructs at thrC contained the left end of ICEBs1 and extend to immediately before helP (thrC::helpΔ; Figure 1C) or to the end of helP (thrC::helP+; Figure 1D).