TATA box is seen in -
Ans. is 'a' i.e.t Promoter regiono These are the consensus sequences of DNA present on same chromosome, which is to be transcribed. These are - Promoter-proximal sequences (or simply promoters):- These are consensus sequences, which lies close to the initiation site of transcription. These can be divided into : -i) Promoters which define where transcription is to commence These are -TATA Box (Hogness box) It is nearly identical to that of pribnow box of prokaryotic promoter region. It is found - 25 base pairs i.e. 25 bp upstream (towards 5l end) from transcription initiation site.Initiator sequence (Inr)Is is found -3 bp (upstream) to +5 bp (downstream) from initiaton site.Down stream promotor element (DPE)It is found -25 bp (downstream) from initiation site. It is the only exception ofpromoter sequences, which is a part of structural gene itself.# The human (eukaryotic) RNA polymerase cannot bind to these promoior directly. Transcription factor IID{TFIID) directs the binding of RNA polymerase to promoter sequence. TF II D is made up of two components : TATA binding protein (TBP) and TBP associated factors (TAFs). The TATA box is bound by TBP subunits of TF II D and directs the binding of RNA polymerase. Inr and DPE are bound by TAF subunits of TF II D to direct the binding of RNA polymerase,ii) Promoters which define how frequently transcription will occur These are - GCbox;- It is found anywhere between -75 to -25 bp from initiation site. It binds to SP-1 protein.b) CAA T boxIt is found at -7 5 bp from initiation site. It binds to C A AT binding transcription factor (C T F). Enhancers :- These are DNA sequences that increase the rate of initiation of transcription by RNA polymerase II. These are located far away from the initiation site. There sequence is called 'response element' that bind to specific transcription factors (TFs), i.e. enhancer-binding transcription factors and function as transcription activators. Silencers (or Repressors) :- These sequences decrease transcription.Trans-acting factorso These are various proteins/factors encoded by DNA sequences genes present on different chromosome, i.e. on chromosome other than to be transcribed, These are -General transcription factors These facilitate binding of RNA polymerase II to promoter-proximal sequence and help to form pre-initiation complex (PIC). Example are TFIIA, TF IIB, TFIID, TFIIE, TFIIF, TF IIH;Coactivators These regulate the rate of transcription by binding to TF, e.g. TAF subunit ofTFII D, HAT, HD AC.ActivatorsThese bind to GC Box or CAAT box, e.g. SP-1 and CTF which bind to GC box and CAAT box respectively.Factors that bind to enhancer or silencers e.g. HRE binding protein.
Promoter region
Palindromic region
Enhancerregion
Silencer region
Molecular Genetics