Expression of nuclear tRNA(Tyr) genes from Arabidopsis thaliana in HeLa cell and wheat germ extracts.

The transcription of thirteen Arabidopsis tRNA(Tyr) genes in a tRNA gene cluster was studied in HeLa cell nuclear extracts. All tRNA(Tyr) genes are efficiently transcribed. Initiation of transcription starts at adenosine residues at positions -5 or -6, and termination occurs at an oligo(T) stretch located 17 to 21 bp downstream of the 3' end of the structural genes depending on the gene studied. Maturation of intron-containing pre-tRNAs was compared in HeLa cell and wheat germ extracts and revealed that 5' and 3' end processing precedes splicing in both systems. Two pre-tRNAs which carry mutations in the mature domain are not processed at all in the HeLa extract, whereas one of them matures with low efficiency in the wheat germ extract. The thirteen pre-tRNAs(Tyr) possess highly conserved intron sequences of 12 nucleotides. Twelve of these introns are efficiently excised, whereas one is removed at a reduced rate, possibly due to a slightly destabilized extended anticodon stem.