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

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Abstract
Higher plant chloroplasts provide the only experimentally validated example of functional tRNA genes that are disrupted by group II introns. Here, precursor transcripts for tRNAGly(UCC), tRNAVal(UAC), and tRNAAla(UGC) were investigated for processing of 5′ leader and 3′ trailer sequences in vivo. Use of intron-specific primer pairs and inclusion of a barley chloroplast splicing mutant specifically allowed us to evaluate the potential effect of intervening sequences that disrupt tRNA secondary and tertiary structures. The data suggest that (1) neither integrity of the dihydrouridine nor the anticodon domain is required for the nucleotidyltransferase-mediated addition of 3′-terminal CCA; (2) interruption of these two structural elements by group II introns does not interfere with nucleotide-specific 5′ maturation 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.