The retrovirus pol gene encodes a product required for DNA integration: identification of a retrovirus int locus.

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Abstract
Cloned spleen necrosis virus DNA was mutagenized to identify a region of the retrovirus genome encoding a polypeptide required for integration of viral DNA. Five plasmids bearing different lesions in the 3'' end of the pol gene were examined for the ability to integrate or replicate following transfection of chicken embryo fibroblasts. Transfection with one of these DNA resulted in the generation of mutant virus incapable of integrating but able to replicate at low levels; this phenotype is identical to that of mutants bearing alterations in the cis-acting reigon, att. To determine whether the 3'' end of the pol gene encodes a protein that interacts with att, a complementation experiment was performed. Cells were first infected with an att- virus and then superinfected with the integration-deficient virus containing a lesion in the pol gene and a wild-type att site. The results showed that the att- virus provided a trans-acting function allowing integration of viral DNA derived from the mutant bearing a wild-type att site. Thus, the 3'' end of the pol gene serves as an int locus and encodes a protein mediating integration of retrovirus DNA through interaction with att.