NUCLEAR TRANSPORT OF H1 HISTONES MEETS THE CRITERIA OF A NUCLEAR-LOCALIZATION SIGNAL-MEDIATED PROCESS

We have studied the nuclear transport of H1 histones using the digiton in permeabilization assay system in order to establish the transport r equirements for H1 translocation to the nucleus. Using HeLa cells and fluorescence-labeled calf thymus H1, we show that the H1 nuclear trans port in permeabilized cells requires the addition of cytoplasmic extra ct. Furthermore, it can be blocked by energy depletion and by chilling or by addition of wheal germ agglutinin or by nonhydrolyzable GTP ana logs. Thus, the import of H1 histones follows the criteria established for nuclear import mediated by nuclear localization signals (NLS). Th e distribution of basic amino acids in average H1 sequences, however, does not allow the assignment of a specific element as a classical NLS . (C) 1997 Wiley-Liss, Inc.