Bacteriophage

=Bacteriophage=

A **bacteriophage** is a virus that infects bacteria. It is commonly employed by molecular biologists as a vector for genetic engineering experiments.

Isolating DNA from a bacteriophage can be done using the following protocol:

**1.** Retrieve a culture containing infected bacteria, along with extracellular phage progeny **2.** Suspend the culture in solution and centrifuge, to isolate a bacterial pellet (which is discarded) from the phage-containing supernatant **3.** Suspend the isolated phages in solution, and add polyethylene glycol (PEG) and NaCl to give precipitated phage particles **4.** Centrifuge in a caesium-chloride gradient to give a pellet of phage particles, and then re-suspend the pellet **5.** Use phenol or chloroform extract to remove protein particles **6.** Use RNase to remove unwanted RNA **7.** Use ethanol precipitation to recover phage DNA