Infectious DNA of spleen necrosis virus is integrated at a single site in the DNA of chronically infected chicken fibroblasts.

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Abstract
The infectious DNA of a number of avian leukosis-sarcoma [Rous sarcoma virus strains] and reticuloendotheliosis viruses were digested with nucleotide-specific restriction endonucleases [Hpa I, HindII, HindIII, EcoRI], and the digests were tested for infectivity. All of the enzymes inactivated the viral infectivities except for [Escherichia coli] EcoRI, which did not inactivate the infectivity of the DNA of 2 of the reticuloendotheliosis viruses, spleen necrosis and chick syncytial viruses. The infectious DNA of spleen necrosis virus after digestion with EcoRI had a bouyant density in CsCl solution greater than the density of the high-molecular-weight infectious viral DNA. The infectious EcoRI-digested spleen necrosis virus DNA from chronically infected chicken cells was uniform in size, 10 Mdaltons, which indicated a single site of integration. The infectious EcoRI-digested spleen necrosis virus DNA from acutely infected cells was heterogeneous in size, ranging from 8-14 Mdaltons, which indicated multiple sites of integration. Cells that integrate infectious spleen necrosis virus DNA at a single site apparently survive and multiply; cells that integrate infectious viral DNA at additional sites either die or selectively lose or inactivate the DNA in the additional sites.