The current model for the biogenesis of mirnas involves several distinct steps. An overview of rna virusencoded micrornas exrna full text. While dicer class iii and other simple rnase iii proteins class i have been studied intensively, the class ii enzyme drosha remains to be characterized. Exportin5mediated transport to the cytoplasm is energydependent, using gtp bound to the ran protein. Rna polymerase prefers gg at the initiation site for efficient. Drosha functions together with its cofactor dgcr8 in a heterotrimeric complex known as microprocessor. Lee y, ahn c, han j, choi h, kim j, yim j, lee j, provost p, radmark o, kim s et al 2003 the nuclear rnase iii drosha initiates microrna processing.
The ribonuclease drosha requires a dedicated doublestranded rna binding. Micrornaindependent roles of the rnase iii enzymes drosha. The rnase iii drosha is the core nuclease that executes the initiation step of microrna mirna processing in the nucleus. The third rnase iii, drosha, previously implicated in prerrna ribosomal rna processing, localizes predominantly to the nucleus 28, making it a good candidate for the nuclear processing factor. In addition to the rnase iii proteins dcls in plants and drosha in animals and the double. Dgcr8pasha is an essential cofactor for drosha, a nuclear rnase iii that cleaves the local hairpin structures embedded in long primary microrna transcripts primirnas in eukaryotes.
In the nucleus, there is the initial transcription of the mirna loci and then processing by the rnase iii enzyme drosha. The ribonuclease iii rnase iii enzyme drosha cleaves the flanks of primirnas to liberate. Smad proteins control droshamediated microrna maturation. Drosha and dicer, may collaborate in the stepwise processing of. Here we identify another rnase iii, human drosha, as the core nuclease that executes the initiation step of mirna processing in the nucleus. Drosha asymmetrically cleaves both strands of the hairpin stem at sites near the base of the primary stem loop thus releasing a 60 to 70nucleotide pre mirna that has a 5. Members of the ribonuclease iii superfamily of doublestranded ds rnaspecific endoribonucleases participate in diverse rna maturation and decay pathways in eukaryotic and prokaryotic cells fortin et al. Biogenesis of canonical mirna requires nuclear processing by drosha, nuclear export by exportin 5, and cytoplasmic processing by dicer. Pre mirna hairpins are exported from the nucleus in a process involving the nucleocytoplasmic shuttler exportin5. The biogenesis of mirnas initiates with the transcription of the mirna gene and proceeds with the cropping of the primary transcript pri mirna into a hairpin intermediate pre mirna by the nuclear. Drosha is a nuclear rnase iii enzyme that initiates processing of regulatory microrna. The nuclear rnase iii drosha initiates microrna processing yoontae lee 1, chiyoung ahn, jinju han1, hyounjeong choi, jaekwang kim 1, jeongbin yim, junho lee2, patrick provost3, olof ra.
The nuclear rnase iii drosha initiates microrna processing. The multifunctional rnabinding protein hnrnp a1 is required for processing of mir18a. The ribonuclease drosha requires a dedicated doublestranded rna binding protein to convert long, nuclear primary microrna transcripts into shorter. Below, we describe the reported roles of drosha beyond nuclear pri mirna processing. Most human genes transcribed by rna pol ii polymerase ii contain short exons separated by long tracts of noncoding intronic sequences. Rnase iii enzyme drosha and the dsrnabinding protein. This study reveals an essential role of drosha, dicer, and drosha. Emerging roles of drosha beyond primary microrna processing. The ribonuclease iii enzymes drosha and dicer are renowned for their central roles in the biogenesis of micrornas mirnas. The mirtron pathway generates microrna class regulatory rnas in drosophila. Micrornas mirnas are noncoding rnas with diverse roles in development and pathogenesis.
Mecp2 suppresses microrna processing by binding to digeorge syndrome critical region 8 dgcr8, a critical component of the nuclear microrna processing machinery, and interferes with the assembly of drosha and dgcr8 complex. Although our knowledge of pri mirna processing has significantly advanced in recent years, the precise role of dgcr8 in this pathway remains unclear. First, the mirna gene is transcribed by rna polymerase ii to produce a long pri mirna, which is then bound to the micro processing complex consisting of rna binding protein dgcr8 and the rnase iii drosha. Biogenesis and the regulation of the maturation of mirnas. Human micrornas are processed from capped, polyadenylated transcripts that can also function as mrnas. Narry kim1 1institute of molecular biology and genetics and school of biological sciences, seoul national university, seoul 151742, korea. Nearly 97% of the human genome is composed of noncoding dna, which varies from one species to another. Research open access solution structure of the drosha. The pri mirna is conducted via the nuclear microprocessor complex, which comprises the doublestranded rna dsrnadiscerning digeorgesyndrome criticalregion protein 8 dgcr8 and endonuclease drosha. In addition to their role in generating proteomic diversity through the process of alternative splicing, intronic sequences host many ncrnas noncoding rnas, involved in various gene regulation processes. Although their functions are being unravelled, their mechanism of biogenesis remains poorly understood.
The microprocessor is known to consist of two proteins, rnase iii drosha and dsrnabinding protein dgcr8 28. Pdf the nuclear rnase iii drosha initiates microrna. Changes in these sequences often manifest themselves in clinical and circumstantial malfunction. Hundreds of small rnas of 22 nucleotides, collectively named micrornas mirnas, have been discovered recently in animals and plants.
Rnase iii enzymes are a family of dsrna specific ribonucleases that generate staggered cuts on each side of the rna helix 21. Rnase iii proteins are classified based on domain organization. The nuclear rnase iii drosha cleaves primary mirnas primirnas to release hairpinshaped premirnas that are subsequently cut by the cytoplasmic rnase iii dicer to generate mature mirnas. The ran gtpase binds exp5 and forms a nuclear heterotrimer with premirnas 6,8. Characterization of dgcr8pasha, the essential cofactor. The rnase iii drosha is the core nuclease that executes the initiation step of microrna mirna processing in the nucleus lee et al. Drosha initiates mirna maturation by cleaving the pri mirna to. Like other rnase iii proteins, drosha is a doublestranded rna dsrnaspecific endonuclease that introduces staggered cuts on each strand of the rna helix 1, 2. Drosha is the catalytic subunit of the microprocessor complex, which initiates. Here, we report the xray structure of drosha in complex with the c. Pdf the nuclear rnase iii drosha initiates microrna processing. Microrna maturation is initiated by rnase iii drosha that cleaves the stem loop of primary microrna.
It is possible that since the functional domains between. The nuclear rnase iii drosha initiates microrna processing article pdf available in nature 4256956. Serrate is a novel nuclear regulator in primary microrna. Then the hairpin pre mirna is carried out of the nucleus by the nuclear transport receptor, exportin5 and finally to the cytoplasm 18, 19. Solution structure of the drosha doublestranded rna.
Dgcr8 is a cofactor of drosha, which interacts with and stabilises drosha through its cterminal tail domain and its double. To gain a deeper understanding of the maturation processes, we here ablated the drosha, exportin 5, and dicer genes using the same human cell line. Numerous genes in these nonproteincoding regions encode micrornas, which are responsible for rnamediated gene silencing through rna interference rnailike pathways. Drosha and dgcr8 are necessary and sufficient to cleave many primirnas tested in vitro 2,5. Drosha is a type iii rnase, which has two tandem rnase iii domains that recognise stem loop structures, and is the catalytic subunit of the microprocessor complex 9. Drosha and dicer have both common and unique functions in male germ cell development. Reevaluation of the roles of drosha, exportin 5, and. Calin ga, sevignani c, dumitru cd, hyslop t, noch e. Research open access solution structure of the drosha doublestranded rnabinding domain geoffrey a mueller, matthew t miller, eugene f derose, mahua ghosh, robert e london, traci m tanaka hall abstract background. Previously, it was established that processing of primirnas in the nucleus is mediated by drosha, a rnase iii endonuclease 5.
They found that in colon carcinoma cell line hct116, after dna damage doxorubicine, wtp53 interacts with the drosha complex through its dna binding domain, facilitating the processing of a subset of nine primirnas including primir161. The first evidence of a direct involvement of wtp53 on mirna biogenesis has been described by suzuki and collaborators in 2009. Drosha was the first human rnase iii enzyme identified and cloned 20. Thus, while ancestral rnase iii members are capable of rrna processing, it is unclear whether this ability has been preserved in drosha 69,70. Canonically, the biogenesis of mirna is a multistep process involving both nuclear and cytoplasmic machineries. Rnabinding protein dus16 plays an essential role in. If drosha was necessary for the maturation of rrna, one would imagine that loss of drosha would have a catastrophic effect on cell survival, growth and proliferation. The rnase iii enzyme drosha is essential for microrna. The canonical mirna processing pathway requires the nuclear ribonuclease iii enzyme drosha, the rnabinding partner dgcr8, and the cytoplasmic ribonuclease iii dicer1.
Rnase iii enzymes typically contain both rnase iii domains and dsrnabinding domains dsrbd and are grouped into three classes based on domain organization 2224 fig. Together with partner protein digeorge syndrome critical region 8 dgcr8, it forms the microprocessor complex, which cleaves precursor transcripts called primary microrna to produce hairpin precursor microrna. Thus, the two rnase iii proteins, drosha and dicer, may collaborate in the stepwise processing of mirnas, and have key roles in mirna mediated gene regulation in processes such as development and. Once in the cytoplasm, the premirnas undergo an additional processing step by the rnase iii enzyme dicer 9 generating the mirna, a doublestranded rna aproximately 22 nucleotides in length. This protein, a member of the karyopherin family, recognizes a twonucleotide overhang left by the rnase iii enzyme drosha at the 3 end of the pre mirna hairpin. Mecp2 suppresses nuclear microrna processing and dendritic. Drosha was identified as the primirna processing factor more than a decade. Lack of drosha in the male germ line leads to deficiency in mirna production and male infertility. Lee y, ahn c, han j, choi h, kim j, yim j, lee j, provost p, radmark o, kim s, kim vn 2003 the nuclear rnase iii drosha initiates microrna processing. Nuclear processing is mediated by the rnase iii enzyme drosha dgcr8 digeorge syndrome critical region gene 8 microprocessor complex to generate precursor mirnas premirnas of. Erh as a component of the microprocessor facilitates the. The droshadgcr8 complex in primary microrna processing.
In addition to two rnase iii catalytic domains, drosha contains a cterminal double. Noncanonical functions of microrna pathway enzymes. This cleaved product is then transported into the cytoplasm for a second processing event mediated by another rnase iii enzyme known as dicer. Nuclear processing is mediated by the rnase iii enzyme drosha dgcr8 digeorge syndrome critical region gene 8 microprocessor complex to generate precursor mirnas premirnas of 70 nt in length. Drosha is a member of the ribonuclease rnase iii family. Lee y1, ahn c, han j, choi h, kim j, yim j, lee j, provost p, radmark o, kim s, kim vn.
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