<prompt> Micro RNA transcribed by: PGI Dec 2008RNA polymerase 1RNA polymerase 11RNA polymerase HIDNA polymerase  <response>: 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 midificationrequiresrequiresrequires 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 intronsfollowed byresult 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 DNAwhich 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 4th3 43Micro RNA mi RNA - Harper 27th320This 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 genestranscription 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 27TH348. LIPPINCOT4TH422-24. 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 nucleoplasmRNA 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. 