Nuclear translocation of Fos is stimulated by interaction with Jun throughthe leucine zipper

Jun and Fos, b-ZIP transcription factors, form a heterodimer and bind to DN A enhancer elements, thereby regulating the expression of target genes. The present study was undertaken to investigate the molecular mechanism underl ying nuclear translocation of the Jun/Fos complex. For this pul pose, norma l rat kidney cells were microinjected with a DNA expression vector containi ng wild-type or mutant c- or v-jun together with c- or v-fos, followed by d etection of the subcellular localization of Jun or Fos by immunofluorescenc e staining. The nuclear accumulation of Fos was markedly enhanced by the pr esence of wildtype Jun, but not by Jun mutants lacking nuclear targeting or zipper dimerization functions, implying that Jun and Fos mutually interact via their leucine zippers and translocate from the cytoplasm to the nucleu s using the markedly stronger nuclear localization signal of Jun.