Characterization of a stable eukaryotic cell line expressing the rous sarcoma virus integrase

The Rous sarcoma virus integration protein (IN) is required for efficient integration of viral DNA into the host genome. IN was expressed in mouse C127 cells using a bovine papillomavinus vector. This system utilizes the mouse metallothionein promoter and the SV40 late polyadenylation signal for efficient expression of IN. A stable cell line derived from a single hygromycin-resistant colony was characterized. The expression of IN increased significantly upon Zn²⁺ induction of the metallothionein promoter, but did not respond to "superinduction" protocols. Full-length nonphosphorylated IN was the major product of expression. A minor product resulting from initiation of translation at an internal Met codon was also produced. The expressed IN did not exhibit the polypeptide heterogeneity at its COOH-terminus nor phosphorylation as is seen when IN is immunoprecipitated from virions. Using subcellular fractionation and indirect immunofluorescence, IN was primarily localized to nuclei and in some cells appeared to concentrate at discrete loci within the nuclei.