Coupled RNA processing and transcription of intergenic primary microRNAs.
The first step in microRNA (miRNA) biogenesis occurs in the nucleus and is mediated by the Microprocessor complex containing the RNase III-like enzyme Drosha and its cofactor DGCR8. Here we show that the 5'-->3' exonuclease Xrn2 associates with independently transcribed miRNAs and, in combination with Drosha processing, attenuates transcription in downstream regions. We suggest that, after Drosha cleavage, a torpedo-like mechanism acts on nascent long precursor miRNAs, whereby Xrn2 exonuclease degrades the RNA polymerase II-associated transcripts inducing its release from the template. While involved in primary transcript termination, this attenuation effect does not restrict clustered miRNA expression, which, in the majority of cases, is separated by short spacers. We also show that transcripts originating from a miRNA promoter are retained on the chromatin template and are more efficiently processed than those produced from mRNA or snRNA Pol II-dependent promoters. These data imply that coupling between transcription and processing promotes efficient expression of independently transcribed miRNAs.
Ballarino
Monica
M
University of Rome La Sapienza, P.le A. Moro 5, 00185 Rome, Italy.
Pagano
Francesca
F
Girardi
Erika
E
Morlando
Mariangela
M
Cacchiarelli
Davide
D
Marchioni
Marcella
M
Proudfoot
Nicholas J
NJ
Bozzoni
Irene
I
D045744:Cell Line, Tumor; D005095:Exoribonucleases / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000502:physiology; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D012342:RNA, Small Nuclear / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins; D043244:Ribonuclease III / Q000235:genetics / Q000378:metabolism*
C474043:DGCR8 protein, human; D035683:MicroRNAs; D011506:Proteins; D012333:RNA, Messenger; D012342:RNA, Small Nuclear; D016601:RNA-Binding Proteins; D012319:RNA Polymerase II; D005095:Exoribonucleases; C120903:XRN2 protein, human; C517918:DROSHA protein, human; D043244:Ribonuclease III