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.