Where is mouse DNA assembled? - briefly
In mouse cells, genomic DNA is synthesized and organized inside the nucleus during S‑phase of the cell cycle. The mitochondrial genome is replicated within the mitochondrial matrix.
Where is mouse DNA assembled? - in detail
Mouse genomic DNA is synthesized within the cell nucleus. During the S phase of the cell cycle, replication origins are recognized by the origin recognition complex (ORC), which recruits Cdc6, Cdt1 and the MCM helicase complex. These factors assemble pre‑replication complexes at specific chromosomal sites, establishing the locations where DNA synthesis will commence.
Replication proceeds at discrete nuclear foci often termed replication factories. Each factory contains multiple active replisomes, where DNA polymerase α initiates synthesis with a short RNA‑DNA primer, and polymerases δ and ε extend the leading and lagging strands. The factories are anchored to the nuclear matrix, ensuring coordinated progression of replication forks and facilitating access to nucleotide pools.
Concomitant with strand synthesis, newly replicated DNA is rapidly packaged into chromatin. Histone chaperones such as CAF‑1 deposit H3‑H4 tetramers onto nascent DNA, followed by H2A‑H2B dimers, forming nucleosomes. This nucleosome assembly occurs at the replication fork and continues behind it, restoring higher‑order chromatin structure as replication advances.
Mitochondrial DNA replication is spatially distinct, taking place in the mitochondrial matrix. However, the bulk of the mouse genome—both autosomal and sex chromosomes—is replicated exclusively in the nuclear compartment described above.
Key steps in nuclear DNA assembly:
- Origin licensing by ORC, Cdc6, and Cdt1.
- Helicase activation and unwinding of parental strands.
- Primer synthesis by DNA polymerase α/primase.
- Elongation by polymerases δ (lagging) and ε (leading).
- Nucleosome formation via CAF‑1 and other chaperones.
- Restoration of chromatin loops and topological domains through cohesin and condensin complexes.
Thus, the assembly of mouse DNA is confined to the nucleus, organized around replication factories, and tightly coupled with chromatin reconstitution to preserve genome integrity.