Self-association of coilin reveals a common theme in nuclear body localization

We have found that coilin, the marker protein for Cajal bodies (coiled bodi es, CBs), is a self-interacting protein, and we have mapped the domain resp onsible for this activity to the amino-terminus. Together with a nuclear lo calization signal, the self-interaction domain is necessary and sufficient for localization to CBs. Overexpression of various wild-type and mutant coi lin constructs in HeLa cells results in disruption of both CBs and survival motor neurons (SMN) gems. Additionally, we have identified a cryptic nucle olar localization signal (NoLS), within the coilin protein, which may be ex posed in specific coilin phospho-isoforms. The implications of these findin gs are discussed in light of the fact that other proteins known to localize within nuclear bodies (e.g., PML, SMN and Sam68) can also self-associate. Thus protein self-interaction appears to be a general feature of nuclear bo dy marker proteins.