THE ENZYMATIC SYNTHESIS OF A CIRCULAR DNA-RNA HYBRID

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Abstract
The synthesis of RNA on single-stranded DNA of the bacteriophage [PHI]X174 has been examined by ribonuclease resistance, density gradient centrifugation, and electron microscopy. During the course of the reaction, RNA appears in three regions of the density gradient. One component has been identified with an RNAase-resistant hybrid structure. The other two components are both sensitive to RNAase, one corresponding to free RNA and the other to abortive syntheses. Electron microscopic examination revealed the gradual conversion of the collapsed coil of the single-stranded DNA template to a double-stranded hybrid structure possessing circular morphology. These photographs establish that this RNA-DNA hybrid possesses the appearance and dimensions of a hydrogen-bonded duplex and eliminates the possibility of unpaired aggregates held together by unspecified devices.