Promoter :
Eukaryotic promoter define as the reason of the transcription unit that promote or support transcription having proper control. They are produced or activated region that can support transcription at 3 types of RNA polymerase. The promoter for Rna polymerase II usually have following function sequences.
Initiator(INR) : It is the region that contains start point ( of transcription) . It has general form of Py2CAPy5 . It is recongnised by RNA polymerase II. The start point depends on the location of TATA box.
TATA box : It is consensus sequence of 8 bases ( TATAAAAA - eukaryotic TATA box) having only A & T base pair & it is the only consensus sequence that occupies a fixed position in the promoter at 25 . It is usually surrounded by a G-C rich sequence.
CAAT Box : It has the consensus sequence GGGCGG . It is usually located at 90 base pair and may be present in several copies in a promoter. It has been shown that CAAT and GC boxes determine the efficiency of transcription while TATA box aligns RNA polymerase at proper site with the help of the factor TFIID and other transcription factor. Sequence of initiator and TATA box constitute the poor promoter to which transcription factorfactors bind to form initiation complex.
Enhancer: Promoter also have enhancer which stimulate the activity of eukaryotic promoters . Enhancer sequence located 100 or 200 upstream. Which interect with proteins other than RNA polymerase . These are also called upstream activation site.
Silencer: Silencer are regulatory elements that repressed gene expression in eukaryotes like enhancer . Silencer can function a great distance from gene they repressed They are the sites of binding of protein just like enhancer.
