Requirement for membrane potential in injection of phage T4 DNA.

The first stages of infection by phage T4 may be divided into energy-dependent and energy-independent processes. Irreversible adsorption, unplugging, and initial exposure of the DNA terminus may occur at 4 degrees C, or at 37 degrees C in bacteria whose energy-yielding metabolism has been poisoned. DNA injection into the cytoplasm needs higher temperatures and energy from the host cell. The nature of this energy requirements was deduced from the use of metabolic inhibitors. Our results show that T4 DNA injection specifically requires the presence of a protonmotive force across the cytoplasmic membrane of the host. Moreover, the chemical gradient (delta pH) does not appear to be essential, but the membrane potential (delta psi) is required.