 A nucleus typically contains between 1 and 10 compact structures called Cajal bodies or coiled bodies ( CB ) , whose diameter measures between 0 @.@ 2 µm and 2 @.@ 0 µm depending on the cell type and species . When seen under an electron microscope , they resemble balls of tangled thread and are dense <unk> of distribution for the protein coilin . CBs are involved in a number of different roles relating to RNA processing , specifically small nucleolar RNA ( <unk> ) and small nuclear RNA ( <unk> ) maturation , and <unk> mRNA modification . 
