Formation of nuclear matrix filaments by p27BBP/eIF6

p27(BBP)/eIF6 is an evolutionarily conserved protein necessary for ribosome biogenesis which was cloned in mammals for its ability to bind the cytodomain of beta4 integrin. In cultured cells, a conspicuous fraction of p27(BBP)/eIF6 is associated with the intermediate filaments/nuclear matrix (IF/NM) cytoskeleton. The mechanism of this association is not known. Here we show that in epidermis p27(BBP)/eIF6 is naturally associated with IF/NM. To analyze the intrinsic capability of p27(BBP)/eIF6 to generate cytoskeletal networks, the properties of the pure, recombinant, untagged protein were studied. Recombinant p27(BBP)/eIF6 binds beta4 integrin. Upon dialysis against IF buffer, p27(BBP)/eIF6 forms polymers which, strikingly, have a morphology identical to NM filaments. Crosslinking experiments suggested that polymerization is favored by the formation of disulphide bridges. These data suggest that p27(BBP)/eIF6 is associated with the cytoskeleton, and contributes to formation of NM filaments. These findings help to settle the controversy on nuclear matrix. (C) 2002 Elsevier Science (USA). All rights reserved.