Nuclear pore complexes (NPCs) orchestrate cargo between the cytoplasm and nucleus and regulate chromatin organization. NPC proteins, or nucleoporins (Nups), are required for human immunodeficiency virus type 1 (HIV-1) gene expression and genomic integration of viral DNA. I utilize the Ty1 retrotransposon of Saccharomyces cerevisiae (S. cerevisiae) to study retroviral integration because retrotransposons are the progenitors of retroviruses and have conserved integrase (IN) enzymes. Ty1-IN targets Ty1 elements into the genome upstream of RNA polymerase (Pol) III-transcribed genes such as transfer RNA (tRNA) genes. Evidence that S. cerevisiae tRNA genes are recruited to NPCs prompted my investigation of a functional role for the NPC in Ty1 targeting into the genome. I find that Ty1 mobility is reduced in multiple Nup mutants that cannot be accounted for by defects in Ty1 gene expression, complementary DNA (cDNA) production or Ty1-IN nuclear entry. Instead, I find that Ty1 insertion upstream of tRNA genes is impaired. I also identify Nup mutants with wild type Ty1 mobility but impaired Ty1 targeting. The NPC nuclear basket, which interacts with chromatin, is required for both Ty1 expression and nucleosome targeting. Deletion of components of the NPC nuclear basket causes mis-targeting of Ty1 elements to the ends of chromosomes. The mis-targeting suggests that nuclear basket Nups are required directly or indirectly, perhaps as global architects or regulators of chromatin organization to orchestrate Ty1 targeting upstream of Pol III-transcribed genes.Medicine, Faculty ofBiochemistry and Molecular Biology, Department ofGraduat
