![]() ![]() In eukaryotes termination is dependent upon two things a poly (A) signal and a downstream terminator sequence 7. Once it reaches the polymerase it causes dissociation of the mRNA from the polymerase 1. In the rho-dependent pathway a protein known as rho binds to the newly transcribed mRNA and slides along it towards the polymerase. The rho-independent pathway depends on a palindromic termination sequence that encodes a stem-loop structure and once the polymerase encodes this palindromic sequence it pauses and the weak interaction of the RNA-DNA hybrid allows it to dissociate from the polymerase 1. One is the rho-independent pathway and the other is the rho-dependent pathway. In prokaryotes there are two paths that can be taken for termination. Termination is quite diiferent among prokaryotes and eukaryotes also. ![]() In eukaryotes there is a TATA box that is -25 bp from the start site that Rpb4/Rpb7 use to initiate transcription 1. Prokaryotes contain a -10 (pribnow’s box) and -35 sequence that serves as a promoter for the polymerase to bind to and initiate transcription. Promoter sequences vary as well between prokaryotes and eukaryotes. On the other hand Pol II in eukaryotes uses two small subunits Rpb4/Rpb7 to bind and scan the DNA. The sigma subunit is used to loosely bind the DNA and slide along the DNA backbone in search of a promoter. Prokaryotes utilize a transcription factor sigma which is the smallest subunit of the structure that can easilty associate and dissociate from the core subunits. Rpb1 and Rpb2 make up the bulk of the complex 6. Eukaryotic Pol II is made up of 10 subunits. The prokaryotic polymerase is made up of four subunits alpha, beta, beta’, and omega subunits 1. This is probably due to the fact that it takes place in the cytoplasm and is subjected to nuclease degradation.Īnother difference between prokaryotic and eukaryotic transcription are the subunits that make up the polymerases themselves. Prokaryotic transcription is carried out in the cytoplasm, where transcription is coupled with translation 1. Furthermore each eukaryotic polymerase carries out its necessary functions at different locations in the cell. Eukaryotes on the other hand have three polymerases (Pol I, Pol II, and Pol III) that carry out different processes involved in the synthesis of protiens 1. For instance prokaryotes have only one RNA polymerase that carries out the complete process of transcription. Prokaryotic transcription is much simpler than eukaryotic transcription. There are however some marked differences between the two. The active center is also conserved in both prokaryote and eukaryotes. Another conserved domain is the rudder (the loop that is closest to the active center). For instance the bridge helix, which is involved in translocation of the Polymerase in porkaryotes and eukaryotes, is conserved, however the bridge helix in prokaryotes is always bent where as the bridge helix is straight in eukaryotes 6. There are some conserved domains that are found between prokaryotic polymerase and eukaryotic polymerase II. For instance both go through an initiation, elongation, and termination phase. Eukaryotes and prokaryotes follow a common path through transcription. ![]()
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