FIGURE 7.

Transcription, maturation and functions of tRNAs. Type 2 promoter tRNA genes are transcribed by Pol III, possibly involving the facilitated recycling pathway, which allows transcription reinitiation in the absence of TFIIIC (1). Primary tRNAs contain 5′ leader and 3′ trailer sequences (colored lines) and a few human tRNAs contain introns (red line). tRNAs are processed by RNAse P, ELAC2 and TRNT1 (2), as well as spliced in the nucleus (3). Mature tRNAs are exported to the cytoplasm and loaded with amino acids for participating in translation (4). Other functions for tRNAs that were described involve enzymatic processing for yielding tRNA fragments (tRFs) or tRNA halves (tiRNAs) (5). In addition, they can enter alternative functional pathways (6).