  Bacteriophages infect cells by attaching to the outer membrane and injecting
their DNA into the cell.The phage DNA is then transcribed by the cell's
transcription machinery.A number of physical mechanisms by which DNA can be
translocated from the phage capsid into the cell have been identified. A fast
ejection driven by the elastic and electrostatic potential energy of the
compacted DNA within the viral capsid appears to be used by most phages, at
least to initiate infection.In recent in vitro experiments, the speed of DNA
translocation from a lambda phage capsid has been measured as a function of
ejected length over the entire duration of the event.Here a mechanical model is
proposed that is able to explain the observed dependence of exit velocity on
ejected length, and that is also consistent with the accepted picture of the
geometric arrangement of DNA within the viral capsid.
