raku tuumas asuvad piirkonnad, milles on palju mRNA töötlemises osalevaid valke ja RNA-sid, Cajal bodies are spherical sub-organelles of 0.3-1.0 µm in diameter found in the nucleus of proliferative cells like embryonic cells and tumor cells, or metabolically active cells like neurons. They contain proteins and RNA-s involved in the processing of mRNA. They are the main location where snRNP-s are assembled.