NUCLEOLAR LOCALIZATION OF EARLY TRANSFER-RNA PROCESSING

There is little information as to the location of early tRNA biosynthe sis. Using fluorescent in situ hybridization in the budding yeast, Sac charomyces cerevisiae, examples of nuclear pre-tRNAs are shown to resi de primarily in the nucleoli. We also probed the RNA subunit of RNase P. The majority of the signal from RNase P probes was nucleolar, with less intense signals in the nucleoplasm. These results demonstrate tha t a major portion of the tRNA processing pathway is compartmentalized in nucleoli with rRNA synthesis and ribosomal assembly. The spatial ju xtaposition suggests the possibility of direct coordination between tR NA and ribosome biosynthesis.