Several small nuclear and cytoplasmic RNAs are synthesized by RNA polymerase (Pol) III as nascent transcripts that must then migrate through RNA processing, modification, and transport machinery on their trek to becoming mature, functional molecules. The first factor to interact with newly synthesized Pol III transcripts is the La protein. Evidence that this molecular chaperone accompanies precursor tRNAs through various RNA modification and processing events and facilitates the assembly of other transcripts into specific RNPs is reviewed. Although most La is nucleoplasmic, some is nucleolar, and several Pol III transcripts, including precursors of tRNAs, U6 small nuclear RNA (snRNA), RNase P RNA, and signal recognition particle (SRP) RNA, have recently been shown to move through the nucleolus. Modifications found previously on La-associated U6 snRNA, coupled with recent data, now suggest that these modifications occur in the nucleolus, while U6...

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