Complete 5 ' and 3 ' end maturation of group II intron-containing tRNA precursors

Higher plant chloroplasts provide the only experimentally validated example of functional tRNA genes that are disrupted by group II introns, Here, pre cursor transcripts for tRNA(Gly)(UCC), tRNA(Val)(UAC), and tRNA(Ala)(UGC) w ere investigated for processing of 5' leader and 3' trailer sequences in vi vo. Use of intron-specific primer pairs and inclusion of a barley chloropla st splicing mutant specifically allowed us to evaluate the potential effect of intervening sequences that disrupt tRNA secondary and tertiary structur es. The data suggest that (1) neither integrity of the dihydrouridine nor t he anticodon domain is required far the nucleotidyltransferase-mediated add ition of 3'-terminal CCA; (2) interruption of these two structural elements by group II introns does not interfere with nucleotide-specific 5' maturat ion by RNase P; (3) processing intermediates of chloroplast tRNAs can be 3' polyadenylated; and (4) plastid DNA-encoded proteins are not required for 3' and 5' maturation of plastid tRNAs.