Thestock bacteriophage ФX174 was prepared by inoculation of ФX174 into a log phase culture of E.coli.The culture was shaken at 37± 2oC until bacterial turbidity cleared, and the virus stock was centrifuged to remove large cellular debris and then filtered through a 0.2-μm membrane filterto remove remaininghost cell debris. The stock culturewas stored at 2-8oC.