Preinitiation complex RNA polymerase II holoenzyme

the preinitiation complex (pic) large complex of proteins necessary transcription of protein-coding genes in eukaryotes , archaea. pic helps position rna polymerase ii on gene transcription start sites, denatures dna, , positions dna in rna polymerase ii active site transcription.

the typical pic made of 6 general transcription factors: tfiia (gtf2a1, gtf2a2), tfiib (gtf2b), b-tfiid (btaf1, tbp), tfiid (btaf1, btf3, btf3l4, edf1, taf1-15, 16 total), tfiie, tfiif, tfiih , tfiij.

the construction of polymerase complex takes place on gene promoter. tata box 1 well-studied example of promoter element occurs in approximately 10% of genes. conserved in many (though not all) model eukaryotes , found in fraction of promoters in these organisms. sequence tata (or variations) located @ approximately 25 nucleotides upstream of transcription start point (tsp). in addition, there weakly conserved features including tfiib-recognition element (bre), approximately 5 nucleotides upstream (bre) , 5 nucleotides downstream (bre) of tata box.

assembly of pic

although sequence of steps involved in assembly of pic can vary, in general, follow step 1, binding promoter.

the formation of preinitiation complex (pic) analogous mechanism seen in bacterial initiation. in bacteria, sigma factor recognizes , binds promoter sequence. in eukaryotes, transcription factors perform role.