The Perinucleolar Compartment (PNC) was first discovered by doing immunofluorescence of cells using an antibody recognizing the polypyrimidine tract binding protein PTB/hnRNP I (Ghetti et al., 1992) . The PNC is found mostly in transformed cells and is only rarely found in primary cells. This nuclear compartment is of irregular shape with a very variable size ranging from 0.25 to 1 mm in diameter. Analysis using electron microscopes revealed that this structure is composed of thick, 80 to 180 nm in diameter fibers, which are in direct contact with the nucleolus (Huang et al., 1997). Live imaging of cells expressing a green fluorescent protein tagged PTB revealed that the PNC is a dynamic structure moving along the periphery of the nucleolus over time (Huang et al., 1997).

PNC components

Several proteins have been described as being highly enriched within the PNC compared to their normal cellular localization. Most of them are RNA binding proteins such as PTB/hnRNP I (Ghetti et al., 1992), CUG binding protein (CUG-BP/hNab50) (Timchenko et al., 1996) and the KH domain containing protein KSRP which is involved in splicing regulation (Huang, 2000) . Also located in PNC are small RNAs transcribed by RNA polymerase III such as Rnase MRP RNA, hY RNA and Rnase P RNA (Lee et al., 1996; Matera et al., 1995).

PNC function The function of PNC remains largely unknown but the presence of hnRNP proteins and splicing factors suggests a role for this compartment in RNA processing. Moreover, the presence of RNA transcripts that are not derived from RNA polymerase I and the fact that RNA polymerase II inhibitors affect the structural integrity of PNC demonstrate that this structure is likely involved in either transcription or accumulation of newly synthesized RNA for further processing or retention (Huang et al., 1998). However, the exact function of the PNC remain to be investigated.

  • The Perinucleolar Comparment and Malignant Transformation from Dr. Sui Hang (Northwestern University)

  • Sandrah Wolin's Lab Pages-- Image of Cajal and PNC together

  • Published PNC images --from WWW.CELLNUCLEUS.COM


    Ghetti, A., Pinol-Roma, S., Michael, W.M., Morandi, C. and Dreyfuss G. (1992) hnRNP I, the polypyrimidine tract-binding protein: distinct nuclear localization and association with hnRNAs. Nucl. Acids Res. 20 (14): 3671-3678

    Huang, S. (2000) Review: perinucleolar structures. J. of Struct. Biol. 129 (2-3): 233-240.

    Huang, S., Deerinck, T.J., Ellisman, M.H. and Spector, D.L. (1998) The perinucleolar compartment and transcription. J. Cell Biol. 143 (1): 35-47

    Huang, S., Deerinck, T.J., Ellisman, M.H. and Spector, D.L. (1997) The dynamic organization of the perinucleolar compartment in the cell nucleus. J. of Cell Biol. 137 (5): 965-974.

    Lee, B., Matera, A.G., Ward, D.C. and Craft, J. (1996) Association of RNase mitochondrial RNA processing enzyme with ribonuclease P in higher ordered structures in the nucleolus: a possible coordinate role in ribosome biogenesis. Proc. Natl. Acad. Sci. USA 93 (21): 11471-11476

    Matera, A.G., Frey, M.R., Margelot, K. and Wolin, S.L. (1995) A perinucleolar compartment contains several RNA polymerase III transcripts as well as the polypyrimidine tract-binding protein, hnRNP I. J. Cell Biol. 129 (5): 1181-1193.

    Timchenko, L.T., Miller, J.W., Timchenko, N.A., DeVore, D.R., Datar, K.V., Lin, L., Roberts, R., Caskey, C.T., Swanson, M.S. (1996) Identification of a (CUG)n triplet repeat RNA-binding protein and its expression in myotonic dystrophy. Nucl. Acids Res. 24 (22): 4407-4414.