THE BEADED FILAMENT OF THE EYE LENS - AN UNEXPECTED KEY TO INTERMEDIATE FILAMENT STRUCTURE AND FUNCTION

In 1959, an unusual filamentous polymer, now called the beaded filamen t, was described in the lens of the eye. The constituent proteins, ass embly properties and functions of the beaded filament have been elusiv e. The recent publication of the sequences for two major lens filament proteins (CP49 and filensin) and the reconstitution in vitro of struc tures closely resembling beaded filaments, suggests that the beaded fi lament is related structurally to intermediate filaments (IFs). The as sociation of the lenticular chaperones, the alpha-crystallins, with th e filament contributes to the characteristic beaded morphology, as wel l as giving important clues to the function of this unusual filament i n the lens. The recent results have several implications for IF functi on and assembly.