Comparison of diverse transport signals in synthetic peptide-induced nuclear transport

Several investigations have demonstrated the ability of synthetic peptides homologous to the nuclear transport signal of simian virus 40 large T antigen to induce the nuclear transport of nonnuclear carrier proteins. To determine the generality of peptide-induced transport, six peptides with sequences derived from four previously identified nuclear transport signals were synthesized and examined for their ability to induce the transport of mouse immunoglobulin G following microinjection into the cytoplasm of mammalian cells. Peptides containing transport signals from simian virus 40 T antigen, Xenopus nucleoplasmin, and adenovirus E1A proteins were highly efficient at peptide-induced transport, while a peptide homologous to yeast MAT alpha 2 protein was incapable of inducing transport. A short nucleoplasmin peptide that contained only the basic amino acid domain was capable of inducing transport but yielded a much slower rate of transport than a long nucleoplasmin peptide encompassing the previously identified minimal transport signal. The short nucleoplasmin signal exhibited a greater capacity for transport than a peptide homologous to the cytoplasmic mutant T antigen signal when conjugates with a low number of signals coupled per carrier protein were examined. However, the short nucleoplasmin peptide was only marginally more effective than the T antigen mutant peptide when conjugates with a high number of signals coupled per carrier protein were examined.