BISC401 Lecture Notes - Lecture 14: Asparagine, Arginine, Methionine
Document Summary
Cleavage and base modification occur during processing of all pre-trnas; some pretrna are also spliced during processing. Methyl and isopentenyl groups are added to the heterocyclic ring of purine bases, and the (cid:1006)"-oh groups in the ribose of specific residues are methylated. Specific uridines are converted to dihydrouridines, pseudo uridine or ribothymidine residues. The introns in nuclear pre-trnas are shorter than those in pre-mrna and lack the consensus splice site sequences found in pre-mrnas. Splicing of pre-trnas is catalyzed by proteins, not by rnas. A pre-trna intron is excided in one step that entails simultaneous cleavage at both ends of the introns. Hydrolysis of gtp and atp is required to join the two trna halves generated by cleavage on either side of the intron. After pre-trnas are processed in the nucleoplasm, the mature trnas are transported to the cytoplasm through nuclear pore complexes by exportin-t.