The other relevant compartment would be the mitochondrion. Mitochondria are actually vestigial bacteria with their own genomes, and it’s thought that billions of years ago an ancient cell (probably an archaean- the cousins of bacteria) tried to consume the ancestor of the mitochondria but lacked the machinery to actually do the digesting and the two established a symbiotic relationship. Since that instance, the mitochondria have been an essential feature of our cell’s biologies. This allowed the mitochondria to develop an extremely reduced genome containing only 37 genes (most of the genes relevant to mitochondrial function are still in the nucleus). Mitochondria have their own ribosomes and even their own genetic code (sort of). There is also a specialized process for the clearance of diseased mitochondria called mitophagy, which is the subject of many excellent reviews e.g. this, this, and this.
Retroviruses are viruses who have an RNA genome, from which they create a DNA copy through reverse transcription that then integrates into the cell of the host (by which I mean, literally inserts itself into the host cell’s genome and becomes a permanent part of it, in the form of a sequence called a provirus). The proviral sequence itself can then be transcribed in the host cell to produce viral proteins and particles that can go on to spread to the next cell. The most famous retrovirus is HIV-1.
