Function and subnuclear distribution of Rpp21, a protein subunit of the human ribonucleoprotein ribonuclease P

Rpp21, a protein subunit of human nuclear ribonuclease P (RNase P) was clon ed by virtue of its homology with Rpr2p, an essential subunit of Saccharomy ces cerevisiae nuclear RNase P. Rpp21 is encoded by a gene that resides in the class I gene cluster of the major histocompatibility complex, is associ ated with highly purified RNase P, and binds precursor tRNA. Rpp21 is predo minantly localized in the nucleoplasm but is also observed in nucleoli and Cajal bodies when expressed at high levels. Intron retention and splice-sit e selection in Rpp21 precursor mRNA regulate the intranuclear distribution of the protein products and their association with the RNase P holoenzyme. Our study reveals that dynamic nuclear structures that include nucleoli, th e perinucleolar compartment and Cajal bodies are all involved in the produc tion and assembly of human RNase P.