Fig. 6. Schematic summary of coilin and its role in nuclear organization. Human coilin is a protein of 576 aa and contains two nuclear localization signals (NLSa, NLSb) in addition to an arginine/glycine repeat region (RG). Previous work has shown that the N-terminal 92 aa of coilin are necessary for self-interaction and Thus, are important in CB formation (Hebert and Matera, 2000). Additionally, knockout studies demonstrate that full-length coilin is necessary for canonical CB formation (Tucker et al., 2001). The C-terminus of coilin is important in regulating CB number (Shpargel et al., 2003) and for the interaction with some Sm proteins and snRNPs (Hebert et al., 2001) (our unpublished observations). The RG box of coilin mediates direct interaction with SMN and reduction in arginine methylation correlates with Gem formation (Hebert et al., 2001; Hebert et al., 2002; Boisvert et al., 2002). The association of PML bodies with CBs is mediated in part by interactions between coilin and PIASy (this study). Not shown are interactions with Nopp140 (Isaac et al., 1998) and nucleic acids (Bellini and Gall, 1998).