Since the start site is denoted as position +1, the TATA box position is said to be located at about position -25.to the 5 side) of the start site which has the consensus TATA(A/T)A(A/T) and is called the TATA box. Most promoter sites for RNA polymerase II include a highly conserved sequence located about 25–35 bp upstream (i.e.During initiation, RNA polymerase recognizes a specific site on the DNA, upstream from the gene that will be transcribed, called a promoter site and then unwinds the DNA locally.The basic mechanism of RNA synthesis by these eukaryotic RNA polymerases can be divided into the following phases: Initiation Phase However, four to seven other subunits of each eukaryotic RNA polymerase are unique in that they show no similarity either with bacterial RNA polymerase subunits or with the subunits of other eukaryotic RNA polymerases.The genes encoding some of the subunits of each eukaryotic enzyme show DNA sequence similarities to genes encoding subunits of the core enzyme of E.Each of the three eukaryotic RNA polymerases contains 12 or more subunits and so these are large complex enzymes.It transcribes the genes for tRNA, 5S rRNA, U6 snRNA, and the 7S RNA associated with the signal recognition particle (SRP) involved in the translocation of proteins across the endoplasmic reticulum membrane. RNA polymerase III (RNA Pol III) is also located in the nucleoplasm.
RNA polymerase II (RNA Pol II) is located in the nucleoplasm and transcribes protein-coding genes, to yield pre-mRNA, and also the genes encoding small nucleolar RNAs (snoRNAs) involved in rRNA processing and small nuclear RNAs (snRNAs) involved in mRNA processing, except for U6 snRNA.RNA polymerase I (RNA Pol I) is located in the nucleolus and transcribes the 28S, 18S, and 5.8S rRNA genes.Unlike prokaryotes where all RNA is synthesized by a single RNA polymerase, the nucleus of a eukaryotic cell has three RNA polymerases responsible for transcribing different types of RNA. Enzyme(s) Involved in Eukaryotic Transcription
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