Relationship of nuclear membranes with filaments and microtubules

Summary In certain HeLa cells characteristic aggregates of cytoplasmic filaments, microfilaments and microtubules were found which preferentially encompass the nucleus. These structures are intimately associated with the membranes of the nuclear envelope and the endoplasmic reticulum as well as with ribosomes. Starting from this observation, a review is presented which demonstrates the nuclear membranes generally as being a type of membrane with a close relationship to proteinaceous structures of the actin-like type such as microtubules and (micro)filaments. As an explanation for the phenomena observed, it is hypothesized that the formation of such tubules and filaments is nucleated at cytomembraneous surfaces and/or that membrane (and possibly also ribosomal) material can be transformed to such tubular or filamentous structures. The concept of cocrystallization between membranes and the diverse tubular and filamentous categories and of a transformation of membrane protein moieties into such structures is thought to provide a basis for explaining many structural phenomena involving membranes and structures of actin-like proteins.The author gratefully acknowledges the careful technical assistance of MissSigrid Krien and MissMarianne Winter and valuable discussions with his colleagues, Drs. H.Falk, H.Kleinig, U.Scheer, as well as with Drs. M.Moses (Duke University), D. J.Morré (Purdue University), and K.Wolff (University of Vienna). The work was supported by the Deutsche Forschungsgesellschaft.