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. Author manuscript; available in PMC: 2015 Apr 24.
Published in final edited form as: Gene Ther. 1999 Jun;6(6):1006–1014. doi: 10.1038/sj.gt.3300924

Figure 7.

Figure 7

Model for plasmid DNA nuclear import. (a) Sequence-specific nuclear import of SV40 promoter/enhancer containing plasmid DNA occurs in all cell types tested. The SV40 enhancer contains binding sites for ubiquitously expressed NLS-containing transcription factors. Since these proteins 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, allowing the NLS-mediated import machinery to recognize DNA as a substrate and target it to the nucleus. (b) Smooth muscle cell-specific nuclear import is achieved by incorporating DNA sequence elements that contain binding sites for transcription factors that are expressed uniquely in SMCs, such as SRF or certain bHLH proteins that bind to E-boxes. These factors act analogously to the ubiquitous transcription factors to couple the DNA to the NLS-mediated nuclear import machinery.