Index >> Bacteriophages - Part One >> Penetration of Nucleic Acids

Penetration of Nucleic Acids - The processes involved in the penetration of phage nucleic - add into the host cell are tail contraction, penetration and unplugging of the core, and injection of DNA.

a. Tail contraction
The tail sheath contracts becoming shorter and thicker. This contraction takes place by rearrangement of the discs of the sheath. From the 24 discs of 6 subunits each there are now J2 discs of 12 subunits each. Contraction of the tail sheath is similar to muscle contraction ill some. ways.

b. Core penetration and unplugging. The energy produced by the contraction of the tail sheath drives the core tube through the cell wall.

It passes through a central hole in the baseplate, which enlarges on contraction of the tail sheath. It was earlier believed that phage lysozyme, a product of the e gene hydrolyzed the cell wall.

However, e mutant phages were also found to initiate infection. The Core, tube passes only through the cell wall and does not penetrate the plasma membrane.

Here it comes into contact with a membrane component, possibly phosphatidyl glycerol, resulting in/unplugging. Contracted phages can be made to release their DNA by treatment with phosphatidyl glycerol.