FORMATION OF NUCLEAR-BODIES IN CELLS OVEREXPRESSING THE NUCLEAR-PORE PROTEIN POM121

POM121 is an integral membrane protein specifically localized in the p ore membrane domain of the nuclear envelope. We have investigated the intracellular distribution of rat POM121 heterologously overexpressed in monkey COS cells by immunofluorescence and fluorescence digital ima ging microscopy. At low levels of expression overexpressed POM121 was distributed in the nuclear envelope in a punctate fashion, partially o verlapping with the distribution of nuclear pores. At high levels of e xpression, however, the over-expressed protein accumulated in intranuc lear bodies. These bodies represent a novel subnuclear structure, disp laying a defined cylindrical structure and a distinct localization at or adjacent to the inner nuclear membrane. The C-terminal portion of P OM121, which contains a pentapeptide repeat domain common to a subfami ly of related nucleoporins, was sufficient to mediate targeting to the nuclear envelope as well as formation of intranuclear bodies. (C) 199 6 Academic Press, Inc.