Ultrastructural subcellular localization of HIV-1 derived vector genomes without the central DNA Flap (Flap -). MT4 cells 48 hr post-transduction with the HR Flap- vector. DNA Flap defective vector genomes localize on the cytoplasmic side of the nuclear membrane. N = nucleus; ne = nuclear envelope; C = cytoplasm. Images show one low and four high magnification micrographs. The first high magnification micrograph is an enlargement from the low magnification image. The other three are taken from other independent experiments. All are highly representative of the data obtained. Arrows point to clusters of immunogold labeled vector DNA.