The isolation of an infectious A protein--RNA complex from coliphage R17.

The coprecipitate of A protein and RNA which results from acetic acid treatment of bacteriophage R17 has been shown to form two bands after equilibrium density gradient centrifugation in Cs2SO4. The band of higher density, whose position coincides with that of phage RNA prepared by phenolisation possesses neither A protein nor infectivity while the band of lower density which contains both RNA and A protein is infectious for intact E. coli cells. The nature of the bonding between the A protein and the RNA was also investigated.