Molecules and Cells

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Fig. 1.

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Fig. 1. (A) miRNAs are first transcribed to pri-miRNAs by RNA polymerase II (Pol II). Nuclear Drosha (C. elegans DRSH-1)-DGCR8 (C. elegans PASH-1) complex then cleaves pri-miRNAs for conversion to pre-miRNAs. Next, pre-miRNAs are translocated from the nucleus to the cytosol, for cleavage by Dicer (C. elegans DCR-1). One of the strands then forms miRNA-induced silencing complex (miRISC) with Argonaute proteins that unwind the RNA duplex. (B) tRNAs are transcribed by RNA polymerase III (Pol III) to precursor tRNA (pre-tRNA) transcripts, which have 5′-leader and 3′-trailer sequences. The 5′-leader sequence is cleaved by endoribonuclease P (RNase P) and the 3′-trailer sequence is removed by endonuclease Z (RNase Z) for generating mature tRNAs. Dicer may cleave the mature tRNAs to tRNA-derived fragments (tRFs). In mammals, angiogenin (ANG, ribonuclease A) cleaves tRNAs and generates tRNA-derived stress-induced RNAs (tiRNAs), also known as tRNA halves, tRNA halftypes of tRNA-derived small RNAs (tsRNAs). (C) RNA polymerase I (Pol I) transcribes 18S, 5.8S, and 28S rRNAs in the nucleolus, whereas 5S rRNA is transcribed by Pol III in the nucleus. (D) Circular RNAs (circRNAs) are produced by back-splicing of precursor mRNAs that are transcribed by Pol II.
Mol. Cells 2019;42:379~385
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