Nuclear pore complexes are the gateways that regulate traffic between the nucleus and the cytoplasm. The nucleus needs many of these gateways to move large molecules like RNA and ribosomal subunits out and various proteins in, so the nuclear envelope is studded with numerous pores. In a typical eukaryotic cell nucleus, the surface area of the envelope and the demand for fast, selective transport lead to a count in the thousands. Estimates commonly place the number around two thousand, which balances the need for efficient exchange with the physical limits of assembling and maintaining such complexes. If there were only a handful of pores, transport would bottleneck; if there were tens of thousands, the envelope would carry an unrealistically dense array of gateways. So the best approximation for a typical nucleus is about two thousand.

Splicing is the RNA processing step that takes place in the nucleus to remove introns from the pre-mRNA, producing a continuous coding sequence. This occurs in the nucleus because the spliceosome machinery, made of small nuclear ribonucleoproteins (snRNPs) and other proteins, operates on the nascent transcript during maturation, before the mRNA is exported to the cytoplasm. In contrast, 5′ capping and 3′ polyadenylation also happen in the nucleus as part of maturation, and export is the transport of the mature mRNA out of the nucleus to the cytoplasm rather than a processing step within the cytoplasm. Therefore, splicing uniquely represents a nucleus-restricted processing event.

During cell division the nuclear envelope must open up so spindle fibers can reach and attach to the chromosomes. The envelope breaks down in early mitosis when lamins are phosphorylated, causing the nuclear lamina to disassemble and the nuclear pores to disassemble as well. This breakdown creates space for microtubules to interact with chromosomes and ensures they can be properly aligned and separated. After the chromosomes are divided, the envelope re-forms around each set of chromosomes in telophase, restoring the double-membrane boundary and nuclear pores. So, it breaks down during nuclear division rather than staying intact, thickening, or becoming part of the plasma membrane.

Chromatin remodeling complexes use energy from ATP to move or remove histone octamers, changing how accessible DNA is to transcription factors and RNA polymerase. The SWI/SNF remodelers are especially known for actively sliding nucleosomes along DNA or evicting them, which exposes promoter and enhancer DNA and helps initiate or regulate transcription. This ability to open up chromatin by repositioning or removing nucleosomes directly links chromatin structure to transcriptional control, making SWI/SNF remodelers the right example for how chromatin remodeling alters DNA accessibility to regulate gene expression. In contrast, DNA methyltransferases modify DNA methylation without changing nucleosome positions, ISWI remodelers primarily affect nucleosome spacing and higher-order compaction rather than eviction to open chromatin, and topoisomerases adjust DNA supercoiling rather than nucleosome positioning.