Micro RNA transcribed by: (PGI Dec 2008)
Arts : B (RNA polymerase II) & E (Drosha) Micro RNA is transcribed by RNA polymerase IIQ & Drosha.Eukaryotic transcription: DMA-Directed RNA Synthesis ||Consists of| | InitiationElongation TerminationPosttranscriptional midification||requires||requires|requires Binding of protein transcription factors and RNA polymerase to promoter sites at the beginning of a geneLocal unwinding of the DNA helix by RNA polymeraseA termination signal sequenceSplicing of mRNA exons to eliminate non-coding introns|followed by|result in Cleavaga and trimming of preribosomal RNAsSynthesis of a 5'-3' RNA transcript coded for by the DNA template read in the 3'-5' directionRelease of RNA polymerase and newly synthesized transcript from DNA|which is facilitated by Enhancer-binding transcription factors bound to enhancer sequences at sites far from the gene Trimming and base modification in tRNA Addition of a 3' poly-A "tall" and a 5'-7-methyl guanosin "cap" to mRNA "Most miRNA are processed from, RNA polymerase II transcripts of several hundred to thousands of nucleotides in length called Pri- miRNA (for primary' transcript). Within these long transcripts are sequence that fold into hairpin structure. A nuclear RNase specific for double stranded RNA called Drosha acts with a nuclear double stranded-RNA binding protein called DGCR8 in human (pasha in drosophila) & cleaves the hairpin region out of the long precursor RNA generating a pre-miRNAOnce in cytoplasmic ds RNA specific RNase called Dicer act with a cytoplasmic ds RNA binding protein called TRBP in human to further process the pre-miRNA into a ds mi RNA - Molecular Biology by Lodish 4th/3 43Micro RNA (mi RNA) - Harper 27th/320This represent a subset of small RNA {< 1% of total RNA) which play important role in gene regulation.Presently all known miRNAs cause inhibition of gene expression by decreasing specific protein production albeit apparently via distinct mechanismmiRNA are typically 21-25 nucleotide in length & are generated by nucleolytic processing of the products of distinct genes/transcription units. These precursors are single stranded but have extensive intramolecular secondary strcuture.The small processed mature miRNA typically hybridize via formation of imperfect RNA-RNA duplex leading via unknown mehanism to translation arrest.miRNA represent exciting new potential target for therapeutic drug development in human.Transcription - HARPER 27TH/348. LIPPINCOT4TH/422-24. 429The process of RNA synthesis per se is quite similar in prokaryotes & eukaryotes but regulation of RNA synthesis & processing of RNA transcripts are differentQIn bacteria one species of RNA polymerase synthesize all RNAs except for the short RNA primer. But in eukaiyotic cell, there are threeQ distinct class of RNA polymeraseRNA polymerase I: This enzyme synthesizes the precursors of the 28S, 18S & 58S rRNAQ ' in nucleolus (Note : mRNA & tRNA are synthesized in the nucleoplasm)RNA polymerase II: This enzyme synthesize the precursors of mRNA that are subsequently translated to produce protein. It also synthesizes certain small nuclear RNA (Sn RNA) & miRNA.RNA polymerase III: This enzyme produces the small RNA including tRNAQ 5S ribosomal RNA & some Sn RNA.
RNA polymerase 1
RNA polymerase 11
RNA polymerase HI
DNA polymerase
Immunology