One technique for the purification of RNA-protein complexes makes use of these organisms in MS2 tagging. Another technique using these organisms uses pIII and takes advantage of an M13 vector. One form of these organisms, in which the Cro and cl repressors are found, (-5[1])was first isolated by Esther Lederberg. These (10[1]-5[1])organisms (10[1])were used to prove that DNA is genetic material by radiolabeling (10[1])with phosphorus-32 (10[1])and sulfur-35 (10[1])in (10[1])the Hershey–Chase experiment. One variety of these organisms that can undergo a lytic life cycle but not a lysogenic life cycle has a hollow tail and an icosahedral head. Examples of these organisms include T4 and lambda. For 10 points, name these viruses that infect bacteria. ■END■ (10[2])