Capsid internal protein that is probably ejected along with the viral DNA and prevents degradation of viral DNA by the host EcoB and EcoK restriction-modification antiviral defense systems. Internal capsid protein. DarA is required for DarB incorporation into the virions. Phage P1 Dar antirestriction system is composed of Hdf, DarA, DdrA, DdrB, DarB and Ulx. Hdf and DarA are incorporated first in the procapsid in a co-dependent manner, followed by DarB, DdrB and Ulx. Belongs to the helicase family.