This same process in eukaryotes creates a slightly larger bubble (about -12 to +4) and is completed by the associated TFIIH and its helicase activity in eukaryotes ( Gnatt, et al, 2001). The processes of binding to the template strand and unwinding the double stranded DNA to form a transcription bubble (from about -12 to +2) is performed by the RNA polymerase holoenzyme ( Vassylyev, et al, 2002). Eukaryotes maintain an association with the transcription factors, with the exception of the mediator complex, throughout elongation as these are necessary for an actively transcribing enzyme.Īs a result of only binding one transcription factor, the bacterial enzyme must perfom many of the common actions of transcription without the aid of additional subunits used by eukaryotes. This leads to a conformational change in the transcribing RNA polymerase. Unlike the process in eukaryotes, the transcription initiation factor dissociates from RNA polymerase following the start of the elongation phase ( Vassylyev, et al, 2002). Eukaryotes require the assembly of a number of transcription factors, including TFIIB, -D, -E, -F, and -H as well as a mediator complex to begin transcription ( Armache, et al, 2003). The sigma factor binds to promoter regions and to bacterial RNA polymerase to initiate transcription (Vassylyev, et al, 2002). The binding of various promoter regions to the transcription factors associated with RNA polymerase allows for greater regulation of transcription regulation.Īs mentioned, only one additional subunit, or transcription factor, is required for promoter recognition in prokaryotes. Other promoter elements are found in different eukaryotic promoter regions. Eukaryotic promoters may contain this combination of recognition sites, but it is not a necessity. An initiator element is located between the -3 and +5 region. A conserved TATA sequence is located at approximately the -25 position upstream of the start site. Several conserved regions do exist, however. The eukaryotic promoter is far more complex and variable than the prokaryotic promoter. These key promoter regions are recognized by the σ subunit of RNA polymerase. The -10 site has a consensus nucleotide sequence of TATAAT and the -35 consensus sequence is TTGACA ( Vassylyev, et al, 2002). There are two key regions that are found within a prokaryotic promoter are located -10 and -35 base pairs upstream from the first transcribed nucleotide. The promoter regions that are upstream of genes are also different in eukaryotes and prokaryotes. II transcribes mRNA and snRNA, and RNA pol. RNA polymerase I is responsible for transcribing rRNA, RNA pol.

In eukaryotes, the RNA polymerase is a large 12 subunit complex, and three separate RNA polymerases are found. In eukaryotes, it is a 4 subunit complex, and one polymerase is responsible for the transcription of all types of RNA. The first major difference is the RNA polymerase itself. The overall process of transcription is conserved between prokaryotes and eukaryotes, but a number of the details of this process are remarkably different.

Bacterial promoter consensus sequences