Indeed long PROMPTs were identified only upon stabilization of the exosome, but it seems likely that these transcripts may otherwise be processed into shorter RNA, such as the PASRs or the TSSa-RNAs, and act locally.
They transcribe short hairpin RNAs (shRNA) that, after being processed into short interfering RNAs (siRNAs), mediate the degradation of the target mRNA.
The second stage, expression and processing, involves transcription and cleavage of long primary transcript of a CRISPR locus (pre-crRNA) that is processed into short crRNAs.
miRNA precursors originate from stem loop containing primary transcripts (pri-miRNAs) and are processed into short double-stranded hairpin RNAs (pre-miRNAs) by Drosha, a RNAse III enzyme.
Interestingly, BORDERLINE is processed into short RNAs (brdrRNAs) by Dicer, a type-III RNase implicated in aging and senescence [ 90- 92].
miRNAs are processed from non-coding genes that produce single stranded precursors with relatively stable hairpin secondary structures that are processed into short, mature miRNAs by Dicer-like proteins.
Recently, it was shown that APLP is processed into short Aβ-like peptides (APLP1β25, 1β27 and 1β28) [ 28] and that the concentrations of CSF APLP1β25 and 1β27 were decreased while the concentration of CSF APLP1β28 was unchanged in four different PS1 mutation carriers [ 32] leading to an increased APLP1β28 to total APLP1β ratio [ 28].
They are first transcribed by RNA polymerase II as long primary miRNA molecules (pri-miRNAs) before being processed into short hairpin RNAs of ~70 nucleotides known as pre-miRNA by Drosha (RNase III enzyme) and DGCR8 (DiGeorge syndrome critical region 8) [ 19].
The enzyme Dicer is one of the several proteins involved in RNA interference, whereby double-stranded RNA (dsRNA) is processed into short (around 22 nt) RNAs that specifically bind to complementary messenger or viral RNAs, leading to their degradation or to the repression of their translation.
In particular, tRNA is processed into shorter forms termed tRNA fragments (tRFs) [ 12, 13].
