Nuclear envelopes: Structure and biochemistry of the nuclear envelope

Publisher Website
Google Scholar
Abstract
The ultrastructure of the nuclear evelope is described in various cell types with special emphasis on its pore complexes (p.c.). The architecture of the p.c. is defined against the properties of other membranous pore formations. Evidence is presented that the non-membranous p.c. components contain ribonucleoproteins but do not represent the attachment sites of nuclear chromatin. The possible dynamic nature of the p.c. material is discussed in relation to nucleocytoplasmic translocation processes. DNA of the nuclear genome is firmly attached to interporous sections of the inner nuclear membrane. The stability of this attachment is demonstrated, and chemical and conformational characteristics as well as periods and kinetics of replication are given for both isolated membrane DNA and the corresponding chromatin in situ . The membrane-associated chromatin is dominated by a heterochromatinous character; it does not represent a transitory membrane interaction of replicating DNA. It is hypothesized that membraneattachment of specific regions of the chromosomes are a means to their ordered arrangement during interphase and prophase. Structure, lipid, protein and enzyme pattern of the nuclear membranes, as well as the incorporation kinetics, underline the relationship to the endoplasmic reticulum.