Order and intracellular location of the events involved in the maturation of a spliced tRNA.

Microinjected frog oocytes were used to analyse the RNA processing steps which lead to the appearance of a mature cytoplasmic tRNAtyr molecule. The results show that removal of the intervening sequence from within a yeast tRNAtyr precursor, excision of extra 3' and 5' nucleotides, addition of a 3'-terminal CCA and modification of at least seven ribonucleotides all occur in the nucleus before the tRNAtyr is transported to the cytoplasm. Moreover, we find that the ribonucleotide modifications occur in a strict order which precisely correlates with the size alterations of the tRNAtyr precursor.