<P> Most proteins, ribosomal subunits, and some DNAs are transported through the pore complexes in a process mediated by a family of transport factors known as karyopherins . Those karyopherins that mediate movement into the nucleus are also called importins, whereas those that mediate movement out of the nucleus are called exportins . Most karyopherins interact directly with their cargo, although some use adaptor proteins . Steroid hormones such as cortisol and aldosterone, as well as other small lipid - soluble molecules involved in intercellular signaling, can diffuse through the cell membrane and into the cytoplasm, where they bind nuclear receptor proteins that are trafficked into the nucleus . There they serve as transcription factors when bound to their ligand; in the absence of a ligand, many such receptors function as histone deacetylases that repress gene expression . </P> <P> In animal cells, two networks of intermediate filaments provide the nucleus with mechanical support: The nuclear lamina forms an organized meshwork on the internal face of the envelope, while less organized support is provided on the cytosolic face of the envelope . Both systems provide structural support for the nuclear envelope and anchoring sites for chromosomes and nuclear pores . </P> <P> The nuclear lamina is composed mostly of lamin proteins . Like all proteins, lamins are synthesized in the cytoplasm and later transported to the nucleus interior, where they are assembled before being incorporated into the existing network of nuclear lamina . Lamins found on the cytosolic face of the membrane, such as emerin and nesprin, bind to the cytoskeleton to provide structural support . Lamins are also found inside the nucleoplasm where they form another regular structure, known as the nucleoplasmic veil, that is visible using fluorescence microscopy . The actual function of the veil is not clear, although it is excluded from the nucleolus and is present during interphase . Lamin structures that make up the veil, such as LEM3, bind chromatin and disrupting their structure inhibits transcription of protein - coding genes . </P> <P> Like the components of other intermediate filaments, the lamin monomer contains an alpha - helical domain used by two monomers to coil around each other, forming a dimer structure called a coiled coil . Two of these dimer structures then join side by side, in an antiparallel arrangement, to form a tetramer called a protofilament . Eight of these protofilaments form a lateral arrangement that is twisted to form a ropelike filament . These filaments can be assembled or disassembled in a dynamic manner, meaning that changes in the length of the filament depend on the competing rates of filament addition and removal . </P>

Where is the genetic material of a cell located why is it called so