ABSTRACT. A method has been developed to isolate pure preparations of nuclei in high yield from commercially available viable rice embryos (germ), employing extraction with buffer solution containing glycerol (without detergent) and polyamine, followed by centrifugation on a 30% Percoll cushion. The intactness of the isolated nuclei was confirmed by light microscopy as well as electron microscopy. The protein profiles of both whole nuclei and nuclear extracts obtained by SDS-PAGE, organellar marker enzymeactivities, DNAand RNA analyses, and in vitro RNAsynthesis, all indicate that the highly purified nuclei are isolated from rice embryos.The biosynthesis of proteins encoded by the nuclear genomeconsists of sequentially oriented networks compartmentalized in the cell; DNAtranscription and RNA processing occur in the nuclei and subsequent RNA transport and translation of mRNA in the cytoplasm. Although the detailed mechanisms of each of these steps has been the subject of intensive cellular and molecular biological studies, RNAsynthesis in the nuclei is of particular interest and importance because of the role of proteins specifically involved in the transcriptional regulation. In recent years muchresearch interest has been focused on elucidating the mechanismsof transcriptional regulation using isolated nuclei of plant origin (2, 8, 17). One can thus readily recognize that isolation of intact nuclei is of prime importance to study the import mechanismacross the nuclear envelopes of various regulatory proteins engaged in the transcriptional activities of the nuclear genome. Since signal sequence(s) of amino acids relating to the import of nuclear proteins have been characterized in the mammalian system (4, 18), it is desirable to construct a feasible experimental system using plant materials to advance our knowledge concerning the mechanism(s) operating * To whomcorrespondence should be sent.

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