BIODYNAMICS OF NUCLEAR MEMBRANE AND MATRIX

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The observation of protein mobility on the outer membrane and immobility on the inner membrane of rat liver nuclei suggests that these membranes may in fact be two functionally different compartments. A dynamic outer membrane may be part of a diffusion pathway, important for nuclear glycoprotein biosynthesis and redistribution of mixed function monooxygenase components between endoplasmic reticulum (E.R.) and nuclear compartments. A non-dynamic inner nuclear membrane containing topologically restrained proteins suggests a role for this membrane in processes requiring organic protein structures and stable multi-enzyme complexes, e.g. - transcription, replication, mRNA translocation. Future experiments are designed to pursue these results by using lateral mobility as a probe for nuclear structure, and as a means to evaluate the validity of mechanisms explaining nuclear-intracellular communication. Antibodies to cytochrome P-450 and P-450 reductase, both outer nuclear membrane proteins, provide specific markers for evaluating the role of outer membrane as a two dimensional communication pathway between cell compartments. Investigations of inner nuclear membrane will seek to explore the role of membrane associated structures, e.g. lamins, chromatin, and ribonucleoproteins in anchoring inner membrane proteins. Substances capable of specifically altering each membrane associated component, e.g. DNAase I, micrococcal nuclease, RNAase, proteases, salts, will be examined with regard to effects on lateral mobility. Another aspect of nuclear diffusion to be investigated will be trans-nuclear membrane transport mediated by the nuclear pore complex. Rates of nucleocytoplasmic transport for model dextran compounds and nuclear and non-nuclear proteins of equivalent size will be compared. These investigations may help define energetic requirements and protein three dimensional structure or sequence that enhance transmembrane transport. A new biochemical perspective on nuclear-intracellular communication is now possible because of the observation that nuclear glycoproteins contain a unique oligosaccharide moiety. Using this as a marker it will be possible to explore whether nuclear membrane and cytoskeletal glycoproteins are synthesized at the nucleus or follow the more conventional endoplasmic reticulum-Golgi pathways. It is hoped that these diverse approaches will provide significant new information relating various aspects of nuclear structure to mechanisms of nuclear-intracellular-plasma membrane communication.