Preinitiation complex, molecular model. Transcription factor IID subunits recognize core promoters (DNA) and support preinitiation complex (PIC) assembly for RNA polymerase II-mediated eukaryotic transcription. The image shows the promoter DNA (pink, cyan) and, among other things, the transcription initiation factor TFIID and IIA subunits, the DNA-directed RNA polymerase subunits and a TATA-box-binding protein.