The long and flexible tail of Siphoviridae acts as a molecular machine that ejects the viral DNA from the capsid into the host cell cytoplasm. The ejection system consists of a baseplate, a central tube and a terminator complex which attaches the tail to the phage capsid 
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Upon binding to the host cell surface, the baseplate changes its conformation and triggers genome ejection into the host cell cytoplasm.
The source of the forces that drive viral genome ejection is probably in part due to osmotic pressure imbalance between the virus inside and the host cytoplasm .
Gram(-) hosts:
- Attachment to a host cell outer membrane (OM) receptor.
- Tail tip penetrates into host OM. Virion-associated exolysin (if present) hydrolyzes the peptidoglycan layer.
- Tail reaches host plasma membrane. Possible loss of tail tip.
- Creation (fusogenic activity?) or use of a hydrophilic pore for viral DNA translocation into host cytoplasm.
Gram(+) hosts:
- Attachment to a host cell wall receptor.
- Tip-associated hydrolysis of the peptidoglycan layer.
- Tail reaches host plasma membrane. Possible loss of tail tip. Opening of the cap.
- Creation (fusogenic activity?) or use of a hydrophilic pore for viral DNA translocation into host cytoplasm.