The general process of transcription can be applied to both prokaryotic cells and eukaryotic cells.  The basic biochemistry for each is the same; however, the specific mechanisms and regulation of transcription differ between prokaryotes and eukaryotes.  This section will compare the process and regulation of prokaryotic and eukaryotic transcription.

            Both prokaryotic and eukaryotic transcriptions use a common enzyme, RNA polymerase, to transcribe DNA into RNA.  Prokaryotes utilize one RNA polymerase for all transcription of types of RNA.  In contrast, eukaryotes utilize three slightly different RNA polymerases:  RNA polymerase I, RNA polymerase II, and RNA polymerase III (8).  Each of the three RNA polymerases in eukaryotes is responsible for transcribing a unique type of RNA.  RNA polymerase I, located in the nucleolus, produces ribosomal RNA; RNA polymerase II, located in the nucleoplasm, produces messenger RNA; and RNA polymerase III, also located in the nucleoplasm, produces both ribosomal RNA and transfer RNA (8).  Although they are responsible for the production of different RNA molecules, all eukaryotic RNA polymerases are homologous to one another and to prokaryotic RNA polymerase (2).  

            In both prokaryotes and eukaryotes, transcription begins with the binding of transcription factors to the promoter site on the DNA.  However, a difference in the number of promoter sequences allows for transcription in eukaryotes to be more highly regulated.  Prokaryotes only carry three promoter elements, -10, -35, and the UP elements, whereas eukaryotes carry a wide variety of promoter elements (4).  In addition, the use of enhancers in eukaryotic transcription allows the promoter sites in remote location on the DNA to initiate transcription.  From this information, it can be inferred that transcription in eukaryotes can occur with less stimulation.

            In addition to having more promoter elements, eukaryotic transcription differs from prokaryotic in that the process occurs within the membrane bound nucleus and is therefore a separate process from translation, which takes place in the cytoplasm.  In prokaryotes, the absence of the nucleus enables the processes of transcription and translation to be coupled.  As the RNA is forming via transcription, the protein is being assembled simultaneously via translation.   This is not feasible in eukaryotes since the transcribed RNA must travel outside the nucleus before translation can occur (Stryer). 

            While specific aspects of transcription differ between prokaryotes and eukaryotes, the basic chemistry behind the process is the same.  Both utilize RNA polymerase to catalyze the synthesis of RNA, and while regulation may differ, the ultimate product of transcription in prokaryotes and eukaryotes is RNA.