Chromosomal proteins HMG-14 and HMG-17 are released from mitotic chromosomes and imported into the nucleus by active transport

The high mobility group 14/17 (HMG-14/-17) proteins form specific complexes with nucleosome core particles and produce distinct footprints on nucleoso mal DNA, Therefore, they could be an integral part of the chromatin fiber. Here we show that during the cell cycle these proteins are transiently diss ociated from chromatin, They colocalize with the nuclear DNA in interphase and prophase but not in metaphase and anaphase. They relocate into the nucl eus and colocalize again with the DNA in late telophase, concomitantly with the appearance of the nuclear envelope. Thus, these nucleosomal binding pr oteins are not always associated with chromatin. Using reconstituted nuclei and permeabilized cells, we demonstrate that these two small proteins, wit h a molecular mass <10 kD, are actively imported into the nucleus. We ident ify the major elements involved in the nuclear import of these chromosomal proteins: HMG-14/-17 proteins contain an intrinsic bipartite nuclear locali zation signal, and their entry into the nucleus through nuclear pores requi res energy and the participation of importin alpha. These findings suggest that the cell cycle-related association of HMG-14/-17 with chromatin is dep endent on, and perhaps regulated by, nuclear import processes.