One technique for the purification of RNA-protein complexes makes use of these organisms in MS2 tagging. Another technique (10[1])using these organisms uses pIII and takes advantage of an M13 vector. One form of these organisms, (10[1])in which the Cro and cl repressors are found, (-5[1])was first isolated by Esther Lederberg. These organisms were used to prove that DNA is genetic material by radiolabeling (10[3])with (10[1])phosphorus-32 and sulfur-35 in the Hershey–Chase experiment. (-5[2])One variety of these organisms that can undergo a lytic life cycle but not a lysogenic (-5[1])life cycle has a hollow tail and an (10[1])icosahedral (10[2])head. Examples of these organisms include T4 and lambda. For 10 points, name these viruses that infect bacteria. ■END■ (10[4])