Figure 6. Model for sequence specific nuclear import of plasmid DNA.
(A) Sequence elements and binding sites for transcription factors are shown for the 366 bp SV40 DNA nuclear targeting sequence. (B) Since these transcription factors are synthesized in the cytoplasm, once plasmid DNA has entered the cytoplasm by transfection, injection, or infection, the newly synthesized proteins can bind to the plasmid DNA to form a DNA-protein complex. Thus, the DNA is coated with NLSs from the transcription factors, allowing the NLS-mediated import machinery to recognize DNA as a substrate and target it into the nucleus.