These proteins line the inner surface of viral envelopes and are associated with viral membranes.

A spring-loaded mechanism is responsible for bringing the viral and cell membranes in close proximity that they will fuse.

When HIV infects its target cell it requires fusion of the viral and cellular membranes.

A mitosis-like cell cycle would proceed until the viral membranes dissolved, at which point linear chromosomes would be bound together with centromeres.

The protein spans the viral membrane with an extracellular amino-terminus and a cytoplasmic carboxy-terminus.

As shown in the Figure, the virus escapes the action of these enzymes by fusion between the viral and lysosomal membranes.

They play a crucial role in virus assembly, and interact with the RNP complex as well as with the viral membrane.

Furthermore, the fusion (F) protein is important in aiding the fusion of the host and viral cellular membranes, eventually forming syncytia.

Binding of the protein with a cell's surface receptors, then fusion of the viral and cell membranes must occur before infection takes place.

It is believed that these molecules bind non-specifically to viral and cellular membranes and can result in photo-oxidation of the pathogens to kill them.