T2 and T4 bacteriophage have been exposed to various treatments which are known to release the encapsulated DNA. The unseparated reaction products have been examined by autoradiography. The results indicate the presence of one large subunit of DNA (molecular weight 45 x 106) for each former phage particle. Some smaller subunits of molecular weight 12 x 106 have been observed.

The large subunit is sensitive to very small amounts of DNAase, and is resistant to mixed proteases and cannot be dispersed by banding in cesium chloride density gradients.

The sensitivity to fragmentation by P32 decay and the increase in this sensitivity following heat treatment are best explained by assuming that the large subunit is a duplex of polynucleotide strands over most of its length.

The presence of hypothetical non-DNA interconnections is considered.

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