Mutational analysis of p80 coilin indicates a functional interaction between coiled bodies and the nucleolus.
Coiled bodies are conserved subnuclear domains found in both plant and animal cells. They contain a subset of splicing snRNPs and several nucleolar antigens, including Nopp140 and fibrillarin. In addition, autoimmune patient sera have identified a coiled body specific protein, called p80 coilin. In this study we show that p80 coilin is ubiquitously expressed in human tissues. The full-length human p80 coilin protein correctly localizes in coiled bodies when exogenously expressed in HeLa cells using a transient transfection assay. Mutational analysis identifies separate domains in the p80 coilin protein that differentially affect its subnuclear localization. The data show that p80 coilin has a nuclear localization signal, but this is not sufficient to target the protein to coiled bodies. The results indicate that localization in coiled bodies is not determined by a simple motif analogous to the NLS motifs involved in nuclear import. A specific carboxy-terminal deletion in p80 coilin results in the formation of pseudo-coiled bodies that are unable to recruit splicing snRNPs. This causes a loss of endogenous coiled bodies. A separate class of mutant coilin proteins are shown to localize in fibrillar structures that surround nucleoli. These mutants also lead to loss of endogenous coiled bodies, produce a dramatic disruption of nucleolar architecture and cause a specific segregation of nucleolar antigens. The structural change in nucleoli is accompanied by the loss of RNA polymerase I activity. These data indicate that p80 coilin plays an important role in subnuclear organization and suggest that there may be a functional interaction between coiled bodies and nucleoli.
D000595:Amino Acid Sequence; D001324:Autoantigens / Q000235:genetics*; D002466:Cell Nucleolus / Q000276:immunology / Q000502:physiology* / Q000648:ultrastructure; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism; D004252:DNA Mutational Analysis; D017353:Gene Deletion; D006367:HeLa Cells; D006801:Humans; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics*; D015388:Organelles / Q000502:physiology* / Q000648:ultrastructure; D017411:Ribonucleoproteins, Small Nuclear / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D001324:Autoantigens; D002868:Chromosomal Proteins, Non-Histone; D009687:Nuclear Proteins; D017411:Ribonucleoproteins, Small Nuclear; C047458:fibrillarin; C068921:p80-coilin