1. Yet higher magnification view of the same nucleolus-Cajal body association as in the preceding two screens (Eucalyptus sieberii, high-pressure frozen and freeze-substituted). The Cajal body still looks amorphous. However, there is now strong evidence that it is a very dynamic object, probably built around a core of the protein "coilin", with many other RNA and protein molecules entering and leaving. There is inward traffic from the nucleoplasm and nucleolus and onward traffic to the nucleolus. The Cajal body is emerging as a site where complexes required for maturation of several classes of small RNA and histone molecules are assembled. It is likely that the internal environment of the Cajal body is somehow especially favourable for precursors of these complexes to meet and become assembled into their working form. They then leave, function, and dissassemble, and the components return to the Cajal body for re-assembly. None of the components of the Cajal body is permanent: all are subject to turnover, mostly rapid, except for the coilin, which is more stable than the other transient constituents.

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