Replication of the RNA of Bacteriophage R17

Escherichia coli cells were irradiated with ultraviolet light to stop ribosomal RNA synthesis. After infection of such cells with the single-stranded RNA phage R17, the RNA most rapidly labeled by a pulse of tritiated uridine sedimented in a broad band in the 16S region of sucrose gradients. The effect of ribonuclease on this material and its behavior during a "chase" period in nonradioactive medium suggest that it consists of a core of double-stranded RNA, one strand of which-the viral strand-is continually displaced by a growing strand forming single-stranded tails and ultimately free 27S viral RNA.