Some eukaryotic promoters also have a conserved CAAT box (GGCCAATCT) at approximately -80. The other transcription factors systematically fall into place on the DNA template, with each one further stabilizing the pre-initiation complex and contributing to the recruitment of RNA polymerase II (figure 11.3). The core complex is TFIID, which includes a TATA-binding protein (TBP). These basal factors are all called TFII (for transcription factor/polymerase II) plus an additional letter (A–J). Transcription factors that bind to the promoter are called basal transcription factors. Table 11.1: Locations, products, and sensitivities of the three eukaryotic RNA polymerases.Įukaryotes assemble a complex of transcription factors required to recruit RNA polymerase II to a protein coding gene. Locations, products, and sensitivities of the three eukaryotic RNA polymerases RNA polymerase Small nuclear RNAs have a variety of functions, including “splicing” pre-mRNAs and regulating transcription factors. The tRNAs have a critical role in translation they serve as the “adaptor molecules” between the mRNA template and the growing polypeptide chain. This polymerase transcribes a variety of structural RNAs that includes the 5S pre-rRNA, transfer pre-RNAs (pre-tRNAs), and small nuclear pre-RNAs. RNA polymerase III is also located in the nucleus. RNA polymerase II is responsible for transcribing the overwhelming majority of eukaryotic genes. Eukaryotic pre-mRNAs undergo extensive processing after transcription but before translation. RNA polymerase II is located in the nucleus and synthesizes all protein-coding nuclear pre-mRNAs. (Note that the “S” designation applies to “Svedberg” units, a nonadditive value that characterizes the speed at which a particle sediments during centrifugation.) RNA polymerase I synthesizes all the rRNAs from the tandemly duplicated set of 18S, 5.8S, and 28S ribosomal genes. RNA polymerase I is located in the nucleolus, a specialized nuclear substructure in which ribosomal RNA (rRNA) is transcribed, processed, and assembled into ribosomes. This is in contrast to prokaryotes, which regulate genes in an operon structure where one mRNA may be polycistronic and encode for multiple protein products. In eukaryotes, a single gene will produce one gene product as all genes are regulated independently.
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