EXOGENOUSLY INJECTED NUCLEAR IMPORT FACTOR P10 NTF2 INHIBITS SIGNAL-MEDIATED NUCLEAR IMPORT AND EXPORT OF PROTEINS IN LIVING CELLS/

p10/NTF2 is a cytosolic factor which is required for the translocation step in nuclear protein import in an in vitro assay with digitonin-pe rmeabilized cells. To study the functional roles of p10/NTF2 on protei n transport between the nucleus and cytoplasm in living cells, recombi nant p10/NTF2 was micro-injected into cultured mammalian cells, Cytopl asmically injected p10/NTF2 strongly inhibited the nuclear import of c o-injected NLS-containing substrates in a dose-dependent manner but ha d no effect on the diffusive import of small non-nuclear proteins, Mor eover, when injected into the cell nucleus, p10/NTF2 inhibited the nuc lear export of NES-containing substrates, The results suggest that the nuclear import factor p10/NTF2 may also be involved in the nuclear ex port of proteins and that the protein transport efficiency between the nucleus and cytoplasm may be regulated by the intracellular level of p10/NTF2.