Subcellular localization of avian sarcoma virus and human immunodeficiency virus type 1 integrases

The composition and subcellular trafficking of subviral preintegration complexes are reported to vary among the different retroviruses. The process by which the avian sarcoma virus (ASV) preintegration complex gains access to target chromatin remains unknown. Here we report that ASV integrase (IN) expressed as a fusion to beta-galactosidase accumulates in the nuclei of transfected COS-1 cells. In contrast, human immunodeficiency type 1 (HIV-1) IN-beta-galactosidase fusions expressed similarly are predominantly cytoplasmic. To identify the region of ASV IN that specifies nuclear localization, various subdomains of the protein were expressed as beta-galactosidase fusions and their subcellular locations were assessed cytochemically and by indirect immunofluorescence. These analyses showed that the ASV IN protein possesses a functional nuclear localization signal that spans amino acids 206 to 235 and displays limited homology with known nuclear transport signals.