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membrane-free nuclei were capable of synthesizing polyphosphoinositides (Cocco et al., 1987) and that some agonists induced changes of inositide metabolism at the nuclear but not at the cytoplasmic level (Martelli et al., 1992), the question arised of the precise localization of this signaling system within the nucleus (Irvine and Divecha, 1992). In fact, it appeared of fundamental interest to determine whether the inositides and the related enzymes are restricted to the nuclear envelope membranes, or localized at DNA-containing structures. In the first case, the system could represent an extension of the transduction system located at the cell membrane, in the second, it could be autonomous and involved in the regulation of genomic functions.